low idle renix

completely stock 89 wagoneer, 4.0, auto, 242.
when i start the engine it revs high as normal, (maybe a little to high at the moment at 2000rpm), then comes down to normal maybe 700 rpm, but in 1 - 2 sec intervals it continues to lower untill barely able to idle. like the timing is being retarded to the point it almost wont run.
i have been reading every thread possible about it and have tried what i think is about every check i know of.
the exhaust has a new muffler but no cat at the moment untill i make sure it is running correctly and not rich.
new 02 sensor (tested good), new TPS (tested good, and set at .83 volts with 4.91 volts input), new CTS, cleaned IAT sensor (tested good), MAP sensor (tested good and even tried a spare), new stepper motor and working properly, cleaned all factory grounds and tested good, added extra ground as per recommended by every darn site i can find, new distributer and pulse generater, new cap and rotor, new plugs, new timing chain set, cleaned all the injectors (had an extra set from another jeep and used the best 6 out of 12), new EGR valve, CPS tested good and no trouble starting. it actually is testing higher voltage than normal since i modified it to sit a tad closer to the flex plate. tried swapping ECU from my 87 parts jeep with no difference. i know i am forgetting a bunch of stuff, but my brain is fried right now and very very very frustrated. i have been attacking this thing for the past 3 weeks and have read as much as i could and tried everything i can think of to remedy the low idle. every sensor and electrical connector i can find has been cleaned and tested. fuel pressure is at 30 psi and holds well. every vacuum line i can find has been checked and or replaced. i have checked for vacuum leaks and didnt find any. vacuum tests out around 15. swapped around the 4 relays, and even replaced them with others.
what all controls the ignition timing? i seem to have gotten this thing to run smooth and nice for a few seconds, then as the idle lowers it starts running worse. to me it seems like the timing is being retarded, atleast that is what it is acting like. a lack of power when on test runs. it runs smooth and shifts good, but i know it is lacking power. during some of the testing and such i found that if while running i disconnect the TPS and reconnect it, it will raise the idle to normal. when i test run it the thing runs great and has its power back. as soon as i shut it down and restart it, the problem exists again.
and befor you say to post all the numbers i got from all the testing of all the sensors, i have basically tossed em all in frustration and am at my wits end. but be sure they all tested within specs as per FSM and info from here or other sites.
if you can think of something to try, please post it and i will see if i have done it or will try it. thanks....

Just for giggles, put your volt meter on a low DC volt scale and test your ground on the TPS side of the connector to the battery negative terminal. It is possible to get near zero ohms and still have (what I call) standing voltage in the ground circuit.

Something else you may want to try just for kicks, is testing the ground circuit with the AC volt scale. Some meters will pick up random AC, some won't. I was having some issues with a bad (partially failed) diode in my alternator.

Another cause may be a very small vacuum leak. Enough extra air to make the motor run rich, but not raise the RPM's.

If all else fails try adjusting your throttle plate until there is about a 0.30 gap closed. Takes a little trial and error, but you can hit a sweet spot. Remember every time you adjust the throttle plate stop, you have to readjust the TPS. You are kind of chasing your tail trying to adjust idle with the throttle stop, the ECU is going to adjust, but you may get lucky and hit a sweet spot.

Mine was doing the same, it seemed to be a combination of things that just added up and the ECU was unable to deal with the conflicting inputs. Most of it was my TPS ground though, it shares a ground with many other things, that splice in at various points. No telling how the injectors pulsing and other things interact with the TPS, ECU inputs.

I eventually succeeded. mine now idles steady at around 600 and thumps nicely. But I'll tell you truth, I really don't know exactly how I succeed.

thanks Mud, i will check the ground on the TPS for low voltage in the morning.

i have not checked the plug reading in a couple days since i put another new set it, but i will tomorrow aswell. do another compression check at the same time. but before when i thought it was running rich (smelled like it from the exhaust), the plugs actually looked perfect. a light brown, if not a little greyish at the tip. that started me on the hunt for any vacuum leaks but couldnt find any. all the lines are good, and i have tried the spray trick all over too. but i will check some more.

oh trust me, uncle bob has been doing his thing with the throttle plate all over the place. i have readjusted the TPS so many times i have broken both screws. my 87s screws were 4mm and the 89 waggy has 4.5 screws, so i ended up re threading them to 5mm since i have a bunch of those. they are now allen head cap screws instead of torx.

i have found the spliced in grounds and made sure they were good. i even added (soldered) in another ground wire from the TPS straight to the firewall ground where i added a #4 cable from the neg side of battery to the firewall. before i did that, with key off i had almost zero ohms, key on i had almost 25 ohms. with the new ground spliced in i do not get the high ohms reading with key on. so i think it was a good idea.

i have 3 TPSs to use. 2 old, 1 brand new. the original tested ok but not when i used the anolog meter to check its range. there was a dead spot. second used one (from the 87) checks out good, but i figured i would try a new one and with the new one installed i cannot get the trans side to be in spec when the engine management side is. i set the new one in spec (.82) on the engine management side and still had the problem. so i now have the second used one back in. set at .83V.

i am going to re check the new 02 sensor tomorrow. i can not remember exactly what the reading where before, but i sort of remember them being a little off. higher than normal, not lower. i figured it being new was why it had higher numbers. might just clean the old one and try that back in.

2stix, have you tested the TPSs on the engine side connector instead of the trans side? They're totally independent of each other.

I misspoke earlier, not a 0.30 gap in the throttle plate, a 0.030 gap. big difference. But like you already found out, it is unlikely to help much, if any, anyway.

I stripped back a little insulation on the TPS wires on the TPS side of the connector, then ran the TPS wire over the top of the TB rubber elbow. Makes testing a whole lot easier.

Make yourself a ground from battery negative to the inner fender or radiator cross brace.

I doubt yours is the same, but mine had the ground wires switched. The ground for the transmission half of the TPS and the engine half of the TPS. In effect the engine half of my TPS was grounding through the TCU. Must have been a Monday harness.

Clean the TPS connector with something good, I had a coating of WD 40 inside mine, gave me fits. I use a high quality electronics and relay spray and scrub the inside of the connector pins with a tiny scrub brush.

Check the O2 sensor harness really well where it runs behind the power steering pump bracket. It can cook on the exhaust manifold back there and be almost impossible to see. I've found that on two different Renix XJ's. Both times, I disconnected the bottom engine connectors and pulled that section of harness up for inspection. Both times I ended up rerouting the harness.

I never did add a ground to my TPS circuit, I just fixed the bottlenecks in the harness. The two main ones were the splices, which I removed, cleaned the copper wire re spliced and soldered. Dirty/corroded connectors and I replaced the ground loops at the dipstick holder. One of my ground loops was already soldered, one wasn't and was seriously corroded.

Sorry to send you on this quest, but like I said, I really don't know what the magic answer is, it is likely to be a combination of faults. All I do know is that it can be done and I was eventually successful.

Hopefully you have looked at your air filter, if they get oil soaked, it will also screw with your idle.

Just some ideas.

I don't know exactly why, but vacuum leaks can lower your idle before the vacuum leak gets big enough to raise your idle. My guess is the ECU tries to richen the mixture a little too much to compensate or goes into a little too lean/little to rich cycle and pretty much constantly tries to adjust. kind of high low idle cycles. I've had both low idle and had it cycle between to low and a little too high. Vacuum leak, TPS, TPS wiring or questionable O2 sensor, all seem to cause this. That .8 volts at the engine side of the TPS at idle, is a very small vopltage, doesn't take much to screw it up.

Plugged Cat?

cruiser54, yes, i have tested both sides and compared both sides many times. swapping out different TPS and comparing numbers. pretty much any time i do a change to anything, i then recheck both sides of the TPS. i use little sewing pins poked through the wire insulation at the connectors. at this point i am just leaving the pins in there and recheck the TPS often.

i have messed with the throttle plate in a variety of settings. and as mentioned, it doesnt do any good. the ECU self adjust the idle no matter where i set it.

i have made extra grounds to different areas. firewall, radiator cross brace, ect.

the 02 harnes that also contains the knock sensor and coolat temp sensor wires all run together and are covered with that split plastic sheathing stuff. it is also attached to the block with a strap to keep it from the header. i inspected it pretty good and did not notice any burning or melting, but i will check again when i re check the 02 sensor today.

air filter is new and old one was not oil soaked. some light oil in the throttle body tube where the pleats would trap it, but nothing much. has been cleaned.

the fact that this system is very dependent on grounds and voltage i was concerned about the actual voltage. since the low idle, of course the alternator was not making enough voltage at idle. so i took one of my extra GM truck alternators and replaced the front half of the housing with the jeep one since the mounting points where different. the new 105 amp alternator made a huge diff in voltage output, but no change to running condition.

thanks for the help and tips guys, i will attack it again this afternoon and let you know what i did and came up with. i seriously can not believe this is stumping me like this. i never had this much problem with any other vehicle i have worked on, and i thought i was pretty good at tuning them. i am close to the point of scrapping the jeep and selling all the parts i have been collecting for the build. lift, tires, gears, lockers, ect. if i have not invested all the money in build parts, i would have scrapped this $100 jeep last week.
i figure if i cannot fix it, i have no business owning it. yes i am that frustrated. lol.

no cat at the moment. new muffler, but i made a cheater tube to run while tuning as to not ruin the cat with unburnt fuel. cat is waiting on the shelf.

The O2 harness cooks on the number one exhaust outlet in the front of the motor. Really hard to see it.

There is a fine idle air adjustment in the TB. The adjuster is behind a solid plug on the side of the TB. Adjust the throttle plate so it just barley touches the side of throat (paper thickness clearance). Clean out the idle air bypass through the screw adjuster. Count the turns when you remove the torx screw adjuster for cleaning. I really don't know the function of the fine idle air adjuster, likely emissions. Most come all the way closed from the factory, some are slightly open and allow some air to bypass the throttle plate.

From the sound of your problem this is unlikely to be a solution. Adjustment seldom changes idle more than 50 RPM.

Some guys have had issues with a cracked exhaust manifold. A crack in just the right place and the right RPM can cause a venturi effect that actually sucks a little extra oxygen into the exhaust before the O2 sensor. Not likely but it seems we are grasping at straws here.

Re torque the intake bolts. If an end stud is snapped off, I wouldn't sweat it too much, they don't do much. I've gotten them to seal fine without the end studs, the middle being loose will sure enough screw with your idle. My guess is when a cylinder or two get a little extra air, the system has issues trying to adjust.

Sounds like you have it well in hand and are likely to eventually get it right. I eventually got it licked. Being dogmatic will usually produce results, sometimes even when skill fails.

thanks for the encouragement.

i know where you are talking about with the harness. i checked that while i had the power steering pump off to re seal the res. but i will look again as i really didnt inspect it that well.

i have tried the little adjuster on the side of the TB. i popped out the plug and it seemed to be pretty much tightened all the way in from the factory. i removed it to clean the port. i tried leaving it a little backed out, but it didnt make any difference. so i put it back all the way in.

i know these headers/manifolds have a tendency of cracking, so i have been trying to listen for any exhaust leaks. i have a stethescope with a long tube that use to poke around in all the areas it can fit. while underneath checking 02 sensor i will give a good inspection of the manifold, and tighten all the bolts. the stethescope did let me pin point the rattle which turned out to be a bad timing chain, so that was replaced the other day. now that i have gotten the engine noises down, i am noticing a sort of knock which seems to be coming from the rear of the engine. i should have inspected the flex plate when i had the oil sump off when i replaced the timing chain and rear main seal. i know they tend to crack too. mine was fine when i swaped the transmission last year, but that doesnt mean it didnt crack now. if the flex plate is cracked and making a knock, the knock sensor can be picking that up and retarding the timing. though i have tried zip tying an extra knock sensor to the wire harness and hooking it up to the wire harnes to ECU as to not have it pick up the knock, but it didnt seem to make a difference.
more testing this afternoon.

thanks again for the help and suggestions. i really appreciate it.

so i check all the manifold bolts and the furthest rear one was a bit loose, but i dont think it caused a leak. it made no change after tightening it. i also did not see any cracks, and i also used the stethoscope to try and listen for any leaks all around the intake and exhaust. found nothing.

so i start testing the 02 sensor. unplugged A and B i get 8 ohms. (cold)
once it warms up i retest it unplugged and get 10 ohms. (warm)
seems the hotter it gets the higher the ohm reading.
plugged back together and started, at B and C the voltage is sporadic (analog meter) needle jumps between 1.5V and 4V. when i say sporadic i mean it is not allways from 1.5 to 4 volts. sometimes it only goes up to 3 volts, and sometimes it only comes down to 2 or 2.5 volts. not a perfect rhythm sort of speak. but it is constant.

also tested the fuel pump resister and it was right at 1.1 ohm just as the thing says it should be.
also put in a new fuel filter (wix) just to be thorough.

still no change. maybe even starting to run worse.

Just a shot in the dark. When the idle hits 700 unplug the IAC and see what happens.

Make sure your MAP vacuum line is plugged into the correct hole.

I'm still thinking it is a TPS issue or maybe a vacuum leak. Two most common causes. Maybe check the .8 volt wire all the way back to the ECU. It is common to have the pins in the ECU connector back out, I've found it numerous times.

You said you changed the timing chain. A real long shot, but trim the bottom locking fork for the distributor. You can trim it so you have one half of the locking fork. makes it easy to return it to the factory setting. Turn the distributor counter clockwise slowly and see what happens. Like I said a real long shot, but it isn't beyond the realm of possibility your new timing chain is indexed wrong and the distributor is running out of advance. Somebody posted the advance at idle awhile back, I seem to recall it being around 21 degrees, but I'm old and don't really trust my memory anymore. Trimming one locking fork needs a grinder and a little trial and error, but it can be done without cutting both off. You can actually tune for top end this way and get another 5-10 MPH, the Renix runs out of timing (or air) before it runs out fuel, learned from my autobahn racer days and my 2WD MJ.

Quick test for your timing chain, find number one compression. Curve a piece of welding rod and stick it down the spark plug hole. You can feel when the piston is at the top. May take a few tries, back the harmonic balancer off a quarter of a turn and try again until you are satisfied you have the piston at the top, look at your timing mark, it should be real close to zero. Long shot but it seems we exhausting the normal causes.

Plug off all of the vacuum lines to your intake, except the fuel regulator. Just to eliminate them as a possible contributing factor. I keep a set of short rubber plugs with a screw in the end, in my toolbox, helps to eliminate variables.

Out of ideas for the moment. I haven't heard anything out of EcoMike, he is more Renix savy than I am, especially the sensors. I have his E-Mail if you need it.

For some reason 30 psi fuel pressure sounds low to me, what is your fuel pressure with the vac hose to the fuel pressure regulator disconnected? Also did you check fuel pump volume? with jeep running and tapped into fuel test port ,fuel should come out like gang busters and fill up a gallon can pretty quickly...... Jeep should run also when you are checking volume when using the hose that came with your fuel pressure tester, take gauge off hose and stick open end in can and screw other end to rail..... Also take a sample of fuel and fill up a clear glass, let it settle for a few minutes and see if you have water in your fuel.... or has a odd smell or a weak gas smell......

Have your extinguisher handy and I really would have a helper turning the Jeep on and off .... Hope you find the problem!

It's 12* at idle, but turning the distributor on a Renix doesn't change ignition timing anyway. It does change injector firing timing though..

My xj did the same thing last year. Turned out the egr solenoid wasn't working and the egr was open at idle. Exhaust gasses choking the engine negatively impacting the idle. Plugged the vacuum line to the solenoid and the problem was gone. I will need a new solenoid for emissions testing, but havent dealt with that yet.

i will need to hook up a remote starter switch to try and disconnect the stepper motor at 700 rpm. (no helper)

correct hole meaning the lower hole on the side of the TB? the upper hole has no vacuum, so i am guessing the lower is the correct hole. with it inserted i disconnected it at the MAP and it has good vacuum.

checking the .8 wire all the way to the ECU is a good idea. i have not done that yet. i have tried a different ECU, but didnt check the actual wire. (i hate pulling that ECU)

the timing chain was replaced after all this started and really didnt make much of a change except it does not rattle any longer. it is the factory replacement, not the double roller that comes with 3 key ways. so indexing it wrong is not possible. yes i suppose they could be manufactured incorrectly, but mine lined up correct.

i will try plugging all the vacuum lines/ports at the engine. i have tested most if not all of the lines to make sure they hold vacuum with a mityvac, but it couldnt hurt to double check.

FSM says fuel pressure should be 31psi +/- 2psi. so i the 30 psi should be ok. with the vacuum line disconnected from the reg. i get 39psi. which is also what the FSM says is correct. i did not do any sort of measurement of the volume, but the bleed hose on the gauge squirts out fuel quickly when i push the button. way more than what the engine would need to run thats for sure.
i will take a sample to check for water.
no helper around, but i do keep an extinguisher close by.

cruiser54, good point. i knew the ECU controls ignition timing and the distributor cannot be an adjusting tool, but i did not know the injector timing can be affected. which also reminds me of something i noticed in the distributor. the pulse generator is held in place by a small metal tab stretching across 2 mounting points. but there are three mounting points available. i noticed my old dist. was mounted in the opposite location than the new one. swapping them over will retard/advance the pulse generator location inside the distributor. i will swap the tab and see what happens.

thanks guys for the tips. i know it has to be something so simple. just finding it has gotten me bugged. my wife keeps telling me to bring it to the dealer. ya right, i can only imagine what that service bill would be.
thanks guys. i appreciate your help.

i did install a new EGR valve. the old one wasnt leaking from the exhaust side, but through the diaphragm shaft. it was allowing fresh air into the intake. not a huge amount, but enough to make want to replace it. other than that the old one was working correctly. the new one is also. but good point.

so i tried swaping the distributor pulse generator mounting points and it did make it run better. cold the engine idled good (around 700rpm) then as it warmed up the rpms went down. pretty quickly actually. maybe one minute of warm up with decent idle, then started going down.

i then decided to go back to my roots and check the spark plug readings, and do a compression check.
spark plugs did not have an even burn. they are new plugs with very little run time. just during the past week of testing and such.
#1 = isolator (white part) was dark brown completely.
#2 = isolator was completely white. with just a hint of light brown on one side.
#3 = isolator was half white on one side, light to medium brown on the other.
#4 = isolator was half white on one side, medium brown on the other.
#5 = isolator was half white on one side, light to medium brown on the other.
#6 = isolator was half white on one side, light to medium brown on the other.
all the electrodes (tips) looked the same and were pretty clean. not enough wear to yet to tell anything.

compression check yeilded pretty even and from what i read in a (ahuuummm) chiltons, were in the upper range.
#1 = 155 psi
#2 = 160 psi
#3 = 165+ psi
#4 = 160 psi
#5 = 155 psi
#6 = 165 psi

the #1 and #2 spark plug reading is what concerns me. when i took off the injectors and cleaned them i found a couple that sprayed funny. so i took the ones from the 87 parts jeep and started cleaning those. three were of a different style. similar but slightly different. but after cleaning and checking each spray into a groelch bottle (i love those for saving the carb cleaner) i ended up needing to use one of the ones that looked slightly different. it is on #2 cylinder. and it makes a much louder click than the rest. so i think i am going to re check the rest of the spares and find one that seems to be ok and install them back in. and no i can not afford to go buy 6 new injectors at $52 each right now. i plan to buy some from the guy that many on here have posted links to. (cant remember the site at the moment).

because of the uneven spark plug reading, i am now starting to think it is a fuel management issue, and not so much a sensor/electrical issue. i have a feeling the sensors and ECU are doing their jobs to aid in the poor fuel delivery.
stay tuned.

Take it to the dealer :gee:, that is where I got mine from. Just about the same problems you are describing, the dealer was unable to fix it. The owner said take this XJ and shove it, I paid half his bill and took the XJ. LOL

The snyc sensor really doesn't do much, it is just a rough index for the injector pulse timing. I forgot and left mine unplugged for a couple of months once and never noticed any, if much, difference in the way it ran.

If the EGR is leaking exhaust into the intake at idle it will sure enough lower your RPM's and eventually stall the motor. The solenoid for the EGR is default open for vacuum, if the wire breaks or the solenoid fails it will supply vacuum continuously and the EGR stays open at idle.

Have you looked at the engine temp. sensor on the lower left side of the block and the harness. I've never had one screw up. but have heard some horror stories about them shorting at the sensor or the harness shorting on the exhaust manifold. You really have to be careful how you route the harness near/behind the power steering bracket. The ohm values for the engine temp. sensor are easy to check.

I had a ballast resistor that tested good (ohms) but when it got hot would really stifle the amps. This would cause your fuel pressure to dive when the engine was running and the resistor heated up. Had almost exactly the same thing happen at a fuel pump connector in front of the rear wheel well. Drove me nuts, the wire color changed twice on the way to the fuel pump. You would have likely noticed a drop in fuel pressure while the engine was running, if either of these were an issue.

The ECU adjusts the timing, initial timing can be pretty far off and the motor still runs OK, the ECU compensates over a wide range of initial timing settings. I've hooked up the spark plug cables one off and had the motor still start. It has a wide range of adjustment, but if the initial timing is really off, runs out of timing at the edges of that range.

Just for giggles, find TDC one, line up the timing marks and see if the rotor is pointing near the one spark plug wire . Simple, but I know I've screwed it up before, installing a distributor or even replacing a distributor cap. You get in a rush and/or hectic and bad stuff happens.

Usually the rotor ends up just before one on the distributor cap. Though my 87 and my 88 end up in slightly different spots. the 87 and 88 have a different cam.

what she doesnt get is that the dealer service dept will not give the amount of time and attention to the jeep unless i want to pay hefty for it. and the jeep is not worth the amount the bill would be. i would end up doing the same as the PO of your jeep.lol.

i am sure changing the pulse gen position probably did not actually make a difference. but it did start better that time with a good COLD idle. coincidence i am sure.

my old EGR was actually working properly. it was not leaking exhaust gases into the intake, but actually fresh air. the exhaust port would close perfectly and i was not able to pull air through it while the diaphragm was closed. but the main port was allowing air to seep through the little shaft bushing. is a little air leakage normal? i dont know. but i did notice the new one did also leak just a very small amount too. maybe i got a bad brand new EGR from the parts store. maybe i will ask if i can test another new one at the parts store.

the engine temp sensor (CTS) was one of the first things i looked at. ohms tested about right according to the temp to ohm values. but i ended up installing a new one because the connector was broken. the new one tested good as well. i wanted to get a new IAT but apparently those are non existent anywhere. i cleaned mine as best i could and installed it back into the manifold. the ohms values do change with temp change, but i have no way of getting the correct temp of the intake air to check exact numbers. those two sensors play a big role in air/fuel ratio and idle. so i really payed them attention. i would love to try a new or known good IAT.

i have tried by passing the resister too. no change in pressure or anything. so i think it is ok.

just so happens, yesterday eve i did check distributor position. since i had the plugs out for reading and compression check, i lined up timing mark and made sure number one was at TDC. rotor was pointing at #1 on cap. (i was so hoping it was off a tooth) but all was good. i also installed new plug wires just to complete the system.

i did break down and buy 1 new injector that matched the rest of them. i could not get any of my spares to flow properly on the bench, so i called the parts store and they just so happened to have one. the one i replaced it with was flowing good, but it seemed to flow too much compared to the rest of them. when i installed them back together i hooked up my fuel pressure gauge to purge the rail. i fired it up and noticed the pressure was only reading 28 psi with vacuum connected. disconnected it only had 35. so i pinched off the return line and the pressure shot up to 62 psi instantly. the regulator is not leaking into the vacuum line, but i think it is hold the return open too much. i am betting the spring inside the regulator is getting too weak. i had the parts store order a new one just in case the pump tests good. but since i am getting an instant 62 PSI with the return line pinched off, i am thinking the pump is fine. i hate to throw $70 at a new pressure regulator, but from the numbers i am getting i think i need it.