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slowrider
July 11th, 2005, 21:57
Little help please. My 87 4.0 MJ was idling slow and rough so I cleaned the throttle body ( which was really nasty) and now it idles smoothly but very fast. Any suggestions as to what might cause this? Any help would be appreciated.

8Mud
July 12th, 2005, 00:32
My IAC was stuck closed and somebody had adjusted the throttle stop to compensate. When I cleaned the IAC, it idled pretty high.
Is your IAC stuck open? If you removed it, did you get it to seat flush or is the "O" ring twisted up some.
Did you knock off a vacuum line, when you were doing the job or break one of the plastic vacuum lines?
if you took off the TB, did you use a new gasket? If you re-used the old gasket, did you get the gasket exactly in the original position.
Vacuum leaks or a stuck open IAC (which is actually rare, they usually stick shut), are usually the chief causes of a high idle.

slowrider
July 12th, 2005, 01:46
My IAC was stuck closed and somebody had adjusted the throttle stop to compensate. When I cleaned the IAC, it idled pretty high.
Is your IAC stuck open? If you removed it, did you get it to seat flush or is the "O" ring twisted up some.
Did you knock off a vacuum line, when you were doing the job or break one of the plastic vacuum lines?
if you took off the TB, did you use a new gasket? If you re-used the old gasket, did you get the gasket exactly in the original position.
Vacuum leaks or a stuck open IAC (which is actually rare, they usually stick shut), are usually the chief causes of a high idle.

Thanks for the ideas. I checked the vacuume lines and the gasket but not the IAC, mostly because I'm not sure what IAC stands for :) Another item a freind told me to check was the TPS (that one I recognised) I'll try the TPS tomorrow and if I can figure out what the IAC is I'll check that too.

BIGSLVRXJ
July 12th, 2005, 05:23
If you left the TPS on while cleaning it you may have ruined it. Get a lifetime warranty Borg-Warner one if thats the case(fry em all ya want.) The IAC is your Idle Air Control Motor. It's located right next to the TPS.(the sensor closer to the passenger side on the TB.) You can adjust the idle stop if needbe but you will need to adjust the TPS afterwards.
HTH,
Collin

Dirt
July 12th, 2005, 05:25
Idle Air Control valve that's what controls your idle speed by allowing more or less air into the throttle body. it's on the throttle body a round thing with three wires i think

XJXJ
July 12th, 2005, 07:48
Idle Air Control valve that's what controls your idle speed by allowing more or less air into the throttle body. it's on the throttle body a round thing with three wires i think

Close, it's actually 4 wires because it's a bi-polar stepper motor driven from the ECU. You've gotta get the TPS adjusted AFTER setting a HOT throttle plate idle RPM with the IAC fully closed. Then adjust TPS per spec and go from there. Sometimes the IAC is at fault but other things will affect idle like 02, temp sensors, latch relay and a few other things.

You can pull the IAC out, leave it connected and watch it while switching the ignition on/off. If it moves, it's probably okay. Another way is to simply pull a small vac hose and listen for the RPM to settle back after a few moments. Or, touch the brake power booster and the sudden loss in vacuum will usually cause the IAC to move a little too but that's very subtle to notice with the engine running.

old_man
July 12th, 2005, 07:50
http://www.4x4getaways.com/TPSIAC.jpgHere is a pix to help. High Idle is normally caused by a vacuum leak, but since you were messing with the TB, go ahead and clean the IAC and the orifice inside.

8Mud
July 12th, 2005, 08:36
You can pull the IAC out, leave it connected and watch it while switching the ignition on/off. If it moves, it's probably okay. Another way is to simply pull a small vac hose and listen for the RPM to settle back after a few moments. Or, touch the brake power booster and the sudden loss in vacuum will usually cause the IAC to move a little too but that's very subtle to notice with the engine running.

If you did that, you got really lucky, Jeep has a tool, to keep the piston from flying out the end of the motor, when testing under power. I had a brain fart and tried just what you suggested once and the plunger from my IAC lauched itself about 15 feet across the driveway. The book says if the piston is seprated from the motor, itīs a throw away, Iīve carefully put the piston back in and had it work fine, though I did, move it to the toolbox for a spare and put my spare in the Jeep.

slowrider
July 12th, 2005, 14:33
I'm learning alot about the renix here thanks guys. I've been going through these suggestions and I haven't found it yet. I cleaned the IAC and re installed it and the idle dropped a bit but not nearly enough so I replaced it without change in the idle, I did the visual verification of the IAC and it works. How does cleaning the TB effect the TPS? to clarify "cleaning the TB" I hosed the butterfly and throat with Chemtool and wiped it out with a new rag, I didn't remove it and open it up so I cant see how I could have hurt the TPS but thats my next item to replace. How possible is it that the chemtool got into the small passeges and broke something loose? I did find the small vacuume line on the side with 2 couplers close together and the other hole in the rubber vacuume reciever wide open but plugging the open one and replacing the spliced line didn't effect it. Pulling a vacuume line off made it idle higher. Thanks again and keep those ideas coming.

old_man
July 12th, 2005, 14:37
I think you were describing the vacuum line that runs to the MAP sensor. One of the holes supplies the vacuum, the other is a blind hole. Make sure you have the hose plugged in the right one.

slowrider
July 12th, 2005, 15:08
I think you were describing the vacuum line that runs to the MAP sensor. One of the holes supplies the vacuum, the other is a blind hole. Make sure you have the hose plugged in the right one.

Sounds right. What I'm talking about is rubber, is on the passenger side of the TB and has two ports. On mine the lower one had a vacuume line leading to a control on the firewall (MAP sensor?) and the top one was open. I replaced the existing line and plugged the upper one.

8Mud
July 12th, 2005, 17:06
Most times the throttle plate (butterfly) sits flush with the sides of the bore, there is no gap (or very very little). On the drivers side of the TB there is a lead cap, under the lead cap there is an adjustment for the idle (if the orifice isnīt gummed shut). If the throttle plate is all the way closed and the lead cap is in place, itīs probably not the TB and is a vacuum leak someplace.
I wouldnīt adjust anything on the TB, until Iīve found and fixed the problem. There actually isnīt much at the TB to adjust to lower the idle, if it is at factory settings.
A bad O2 sensor will often, cause the idle to fluctuate (up and down) a couple of hundred RPMīs (also sometimes a very small vacuum leak will do the same).
Try unpluging the vacuum lines one at a time and plugging the nipple on the intake with your finger and see what happens.
If your idle is at 1500 RPMīs thatīs almost always the major vacuum line near the rear of the intake, thats open someplace or has fallen off of your vacuum canister.
800 or 850 actually doesnīt work bad for an idle, thats where I set mine, I often idle and talk on the radio, noticed my battery would slowly discharge at around 500-650 RPM`s, it stays charged at 800-850.
Does your idle change with the motor temp.?
Is your A/C on?

slowrider
July 12th, 2005, 21:58
Most times the throttle plate (butterfly) sits flush with the sides of the bore, there is no gap (or very very little). On the drivers side of the TB there is a lead cap, under the lead cap there is an adjustment for the idle (if the orifice isnīt gummed shut). If the throttle plate is all the way closed and the lead cap is in place, itīs probably not the TB and is a vacuum leak someplace.
I wouldnīt adjust anything on the TB, until Iīve found and fixed the problem. There actually isnīt much at the TB to adjust to lower the idle, if it is at factory settings.
A bad O2 sensor will often, cause the idle to fluctuate (up and down) a couple of hundred RPMīs (also sometimes a very small vacuum leak will do the same).
Try unpluging the vacuum lines one at a time and plugging the nipple on the intake with your finger and see what happens.
If your idle is at 1500 RPMīs thatīs almost always the major vacuum line near the rear of the intake, thats open someplace or has fallen off of your vacuum canister.
800 or 850 actually doesnīt work bad for an idle, thats where I set mine, I often idle and talk on the radio, noticed my battery would slowly discharge at around 500-650 RPM`s, it stays charged at 800-850.
Does your idle change with the motor temp.?
Is your A/C on? Well I don't have AC so thats not it. I've checked the vacuume system over and over and I haven't found much (not that there isn't a problem). Just in case I changed the O2 sensor and NOW the idle is fluctuating where it wasn't before. The lead plug is in place on the TB. A buddy of mine said to reset or clear the computer but he wasn't absolutley sure how to do it . He thinks you disconnect the posative battery cable and hold the key in the crank position for 15 seconds and then start it and let it idle for 15 Min.Anyone know if that's correct for a renix? . I'm going to try a reset and if that doesn't work maybe do a real TB cleaning. Thanks again.

XJXJ
July 13th, 2005, 06:11
Well I don't have AC so thats not it. I've checked the vacuume system over and over and I haven't found much (not that there isn't a problem). Just in case I changed the O2 sensor and NOW the idle is fluctuating where it wasn't before. The lead plug is in place on the TB. A buddy of mine said to reset or clear the computer but he wasn't absolutley sure how to do it . He thinks you disconnect the posative battery cable and hold the key in the crank position for 15 seconds and then start it and let it idle for 15 Min.Anyone know if that's correct for a renix? . I'm going to try a reset and if that doesn't work maybe do a real TB cleaning. Thanks again.

Curious, does an '87 with no AC even have an e-fan?

Very few KAM codes stored in Renix. It doesn't hurt to clear 'em but I don't think it matters much. Just pull battery power with the key-on for a few seconds.

You're gonna need to qualify the system one step at a time.

Cesar
July 13th, 2005, 09:45
I hade a similar problem with my 88 XJ, the thing that solved it was removing the big cable conector at the firewall by splicing the wires, this connector was only used in a couple of years on the jeeps and was discarded because it caused a lot of problems due to corrosion on the terminals.

old_man
July 13th, 2005, 10:01
Probably one of my most valuable diagnostic tools is very uncommon in most people's tool boxes anymore. It is a vacuum gauge. You can buy them for less than $20. It is a great tool. Hooking it to your intake can tell you tons about the health of the engine. Many of the vacuum gauges can also be used for a pressure gauge to measure fuel system pressure as well.

With a vacuum gauge, you can tell in a minute if the problem is a vacuum leak related problem or a computer related problem.

Bender
July 13th, 2005, 11:19
What is the vacuum supposed to be at idle?

How does the vacuum guage tell you if your problem is vacuum related or not? Wouldn't a sensor problem cause the IAC to open slightly which would read the same as a vacuum leak?

georgemu
July 13th, 2005, 11:58
What is the vacuum supposed to be at idle?

How does the vacuum guage tell you if your problem is vacuum related or not? Wouldn't a sensor problem cause the IAC to open slightly which would read the same as a vacuum leak?

CONDITION INDICATION
readings are at idle unless otherwise stated. Gauge readings are in inches
1. Normal Steady at 15 to 21
........................
Drops to 2, then rises to 25 when throttle pedal is rapidly depressed then released.
2. Intake leak Low steady reading less than 10
3. Head gasket leak Gauge floats between 5 and 19
4. Improper idle mixture floats slowly plus or minus 1 ― to 2 ― inches
5. Small spark gap or defective points slight float plus or minus 1 to 1― inches
6. Late ignition timing Approx 2 inches below normal idle
7. Late valve timing 4 to 8 inches below normal idle
8. Worn valve guides Oscillates plus or minus 2
9. Weak valve springs Violent oscillation (plus or minus 5 inches) as rpm increases. Often steady at idle.
10. Sticking valves Normally steady, will intermittently flick downward about 4 inches
11. Leaky valve Regular drop about 2 inches
12. Burned or warped valve Regular, evenly spaced down-scale flick approx 4 inches
13. Worn rings/ diluted oil Drops to 0, then rises to approx 18 when throttle is rapidly depressed then released
14. Restricted exhaust system Normal when first started. Drops to 0 as rpm increases. May eventually rise to approx 18

Bender
July 13th, 2005, 12:08
Would a stroker motor read higher vacuum?

slowrider
July 13th, 2005, 12:14
Curious, does an '87 with no AC even have an e-fan?

Very few KAM codes stored in Renix. It doesn't hurt to clear 'em but I don't think it matters much. Just pull battery power with the key-on for a few seconds.

You're gonna need to qualify the system one step at a time.

You're right there isn't an e fan yet (I have one coming in the mail) Well I tried clearing the codes and it didn't help so I pulled the IAC and the piston is the same size as the original one but the barrel around it has a thinner wall so I'm wondering if thats causing an air leak.

slowrider
July 13th, 2005, 16:19
GOT IT!!! Thanks again for all the suggestions, in the end they led me to the problem. First I've put less than 1000 miles on it after buying it from god only knows what # owner. I finally removed the TB from the intake and gave it a good cleaning and found a large gap around the butterfly, I tried to adjust the stop screw which looks like they adjusted it with a pair of channelocks (threads mangled) and the allen end is also stripped so they evidently decided to just bend the stop ear on the butterfly (pliar marks again) to make it idle insted of cleaning the TB or replacing the stop screw; straitened it out and all is well. It also solved the long cranking before starting problem.

outlander
September 26th, 2014, 13:40
I need to revive this thread to ask how to measure where the throttle stop screw is supposed to be from the factory?
I suspect the PO may have adjusted it....im chasing a high idle on my 89 and want to rule that out

GregGA
September 26th, 2014, 17:03
Automatic trans? Describe what the idle is doing.

Typically, in a Renix it will be bad grounds or TPS out of adjustment or bad.

Tell us more:)

outlander
September 26th, 2014, 17:13
Manual trans.
its idleing around 1300 rpm.....
I have been driving with the IAC unhooked for years because with it hooked up it revs to around 2000 rpm briefly on start up.
I cleaned my TB last night and decided to hook the IAC back up so I think its IAC related but want to rule out the throttle stop screw...
Other than that it runs good....tps is fairly new and adjusted right (did that yesterday)

8Mud
September 26th, 2014, 19:23
All the throttle stop screw does is stop the throttle plate from slamming into the TB bore and eventually cutting a groove in the TB throat. The basic adjustment is so the throttle plate just clears the TB throat.

The thing about the throttle stop screw adjustment is, minor adjustments may hardly be noticeable, the ECU corrects some for the idle change. Minor changes in the stop screw are like chasing your tail, you may get a momentary idle change, but the ECU eventually corrects and it ends up just about the same as before you fiddled with it. The ECU adjusts the pulse band width, fuel ratio and IAC. And any adjustment at the stop screw requires another TPS adjustment.

1300 RPM sounds like a vacuum leak, most likely in a sub system, heating, A/C controls, maybe the purge vacuum line or maybe the vacuum lines for the vacuum canister. I usually make up a handful of short pieces of vacuum line, around two inches long, with a screw in one end and plug off every vacuum inlet on the intake manifold, except the fuel regulator. Process of elimination, if the idle falls, plug them back up one at a time and see which one is causing the high idle, troubleshoot the sub system from there.

Like mentioned the TPS grounds can also cause issues. TPS controls timing and fuel to some degree along with inputs from other sensors. Replacing the TPS sensor may not help if the issue is in the wiring, connectors or the ground points themselves. I even had one idle problem that was from oil in the TPS connector. Some mechanic thought it was a good idea to spray the connector with WD-40 which turned out to be a bad idea. Many of my TPS issues caused what I call hunting at idle, the idle goes up, then down and then back up again, in 2-3 minute cycles. The exception is a really bad (water soaked) TPS then you may get a 2500 RPM idle. Or serious ground issues which may cause a Renix hot start, when the idle flairs way up right after a start. Sticky IAC or even charging system issues can also cause a hot start.

I always start out by plugging off all the unnecessary vacuum inlets on the intake manifold, re-torque the bolts for the intake/exhaust manifold, check the TB for tightness (the gasket shrinks with age) and ohm my TPS grounds. Eight times out of ten it is one of these 3-4 things causing the high idle issues.

You may also want to take a look at your charging system. Many times when my IAC started acting up it was because of a charging or battery issue. Not often a high idle issue, more often a stalling issue, sometimes a hot start issue. The IAC gets sluggish when the charging system is sick, Renix or OBD.

outlander
September 28th, 2014, 00:09
8mud
thank you for your very detailed reply.Can you explain the process of ohm testing the tps grounds and where they are?

8Mud
September 28th, 2014, 03:39
8mud
thank you for your very detailed reply.Can you explain the process of ohm testing the tps grounds and where they are?

The quick method for me is to strip back a little of the insulation on the black ground wire on the TPS side of the connector, set your ohm meter on the X100 scale and ohm test to the battery negative terminal and see how much resistance you have. I usually route the TPS wires over the top of the rubber intake before the TB, this makes the test much more simple.

When/if you find significant resistance, say over 0.5 ohms, you start moving your test up stream from the battery pole. Your trying to isolate the problem, though it may be a *combination* of less than perfect connections. It is usually a problem at a connector or a ground ring, sometimes a splice. Time consuming and a general pain, it is necessary or more often than not you are wasting your time swapping parts out and making adjustments.

Remember cold motor and warm motor (over around 140-160 F.) reacts differently and uses different motor management. Most times a Renix hot start happens on a warm (hot) motor after the XJ has been stopped and then started again while the motor is still hot. A high idle flair on a cold motor is often a sticky IAC or maybe a TPS issue. A high idle on a cold motor around 1500 RPM's is most often a vacuum leak and as the motor warms up the idle may fall some or the idle may cycle a little high and a little low on the warm motor as the ECU tries to adjust.

First thing I'd check if I were you, is the torque on the intake bolts. I have to re-tighten mine every few years (3-5 years). I just had a high idle issue in my 96, it would idle above a thousand RPM and would eventually settle in to 800 or so as the motor warmed up. Turned out to be an intake/exhaust manifold gasket, the bolts had come loose (the rear stud actually fell off) and the exhaust eventually burnt a groove through the gasket. If I'm hunting a high idle issue one of my first thoughts is when was the last time I re-torqued the intake/exhaust manifold. I usually ignore the end studs on the manifold when re-torquing. those thing snap off way to easily. The thing about an intake gasket leak is as the motor warms up the higher than normal idle may go away as the parts heat up and swell/expand or it may get worse as the intake/exhaust parts flex from the heat.

outlander
September 28th, 2014, 22:56
Thanks again.
was poking around today and found a vac leak at the rear ccv line.
now idle is around 1000rpm.(what is spec for a 5 speed?)

tested tps again and found it had a dead spot right before WOT.

BulletMaker
October 1st, 2014, 03:09
GOT IT!!! Thanks again for all the suggestions, in the end they led me to the problem. First I've put less than 1000 miles on it after buying it from god only knows what # owner. I finally removed the TB from the intake and gave it a good cleaning and found a large gap around the butterfly, I tried to adjust the stop screw which looks like they adjusted it with a pair of channelocks (threads mangled) and the allen end is also stripped so they evidently decided to just bend the stop ear on the butterfly (pliar marks again) to make it idle insted of cleaning the TB or replacing the stop screw; straitened it out and all is well. It also solved the long cranking before starting problem.

Ugh, I had this problem with an 89 I bought for the wife. Took me quite a while to find this, oddly enough it was the marks left by the pliers that gave it away.

outlander
October 1st, 2014, 17:00
Gotta love half ass mechanics....