87 high idle is gonna kill this jeep.

I have been dealing with this problem for almost 2 years. I'll start the jeep up and it will fire up at times. But most of the time it takes 2 or 3 cranks and then will rev up to 2500 and stay for maybe 30 seconds and sometimes won't come down and goes to like 3000 and i have to keep starting it up and turning it off until it decides to come down. Now i have no vac leaks I have replaced everything Map, IAC x2, TPS x2. However when i take out my Power Latch Relay it starts up without the high idle. WHY? I ran it for a few weeks and it was fine like that but when the high idle decides to come back it won't go back down unless the Latch relay is back in place....Anyone have any suggestions or Info?

Oh yeah most of the time if it starts up fine i can shut it off and restart and the high idle returns...

I know the TPS was adjustable with the renix era. Did you adjust it?

I'm not going to tell you HOW to adjust it because I do not know....maybe somebody else can chime in with those directions!

yeah its adjusted.

The latch relay keeps power to the computer after shut down to reset the IAC for the next start(drives it wide open). My 87 use to do that, problem was bad connection/ground in the c101 conector located right above the master cylinder. Since I cut all the wires through that connector and soldered them together one at a time, the thing has behaved normal.

I suppose he could try cleaning those connections and then apply diaclectic grease to the connections to keep them clean. Worth trying at the very least.

I did clean and applied the grease to the Relay and swaped it out with the fuel pump relay to make to rule the relay out. I guess i could try and take the wires out of the relay's socket and clean them 1 at a time. Ron is there any way you could get me a pic of where that ground wire is? I know where the harness is but not sure about the c101.

Nevermind i found a diagram.

Mine would have what others have called the typical Renix hot start. Revs up to around 2500 and stays that way for a few seconds too long, up to way too long, when it's hot. Rarely does it when it's cold. One of the reasons Jeep retrofitted Renix era XJ's with an interlock (recall), you can't start it without your foot on the brake. In other words, Jeep never found a total cure. Interlock installation is expensive and time consuming, if they had found a simpler fix, they would have done that.
Mine got way better after I got my starting, charging/battery in order and did a good tune up. The starter sucks down a lot of juice when it's cranking, long cranks at start up aggravate the problem, the IAC needs all juice it can get to work properly. A fresh good battery helped mine the most, at the same time I replaced the brushes in my starter (and cleaned it out). Around the same time replaced my alternator (my old one was dieing of old age slowly). Around the same time I found a flaky TPS ground, actually a splice to ground. Did a tune up.
I think it was mostly the fresh battery, but my typical Renix hot starts, were reduced by about 99 %.
I don't know if it is possible for the IAC alone to run the motor up to 3000, even all the way open and unplugged. A wet TPS will do it, as will a major vacuum leak (like leaving the brake booster vacuum line off).
Some of the old timers have added an extra spring to the TB throttle plate, either for sticky throttle cable insurance or weak throttle plate springs.

check ground wires that attach between the dipstick tube mount and main harness, I fought (and fought) withi high idle on startup, It would be fine if I unplugged the tps, or b+ latch relay when starting and plug it back in after it was running. Did this for some time. Replaced all ground wires, engine to battery,engine to body, engine to firewall, added another from batt to intake and tied in to tps,Iac. Finally found it to be one (cracked,but intact) wire out of the group of grounds at that dam dipstick to harness. It happened when I swapped in my new engine.good luck!

Rambopants said:

I did clean and applied the grease to the Relay and swaped it out with the fuel pump relay to make to rule the relay out. I guess i could try and take the wires out of the relay's socket and clean them 1 at a time. Ron is there any way you could get me a pic of where that ground wire is? I know where the harness is but not sure about the c101.

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If you take the whole relay block off and turn it over carefully, you may find a nasty surprise.

Like mentioned good grounds are critical.

I can't really remember who turned me onto the trick (Zuki Ron I think) , but instead of die electric grease I use contact paste, it actually improves continuity through the connector pins. You have to be careful with the stuff as it is a conductor, no smearing it all over the place like di electric grease. Each pin has to be coated separately with a toothpick or other suitable tool. I found the stuff at a Model train shop they use it before snapping the tracks together. Stuff seemed to really help, with various sensor (very low voltage) connections and for smearing up grounds after a good cleaning.

8Mud said:

If you take the whole relay block off and turn it over carefully, you may find a nasty surprise.

Like mentioned good grounds are critical.

I can't really remember who turned me onto the trick (Zuki Ron I think) , but instead of die electric grease I use contact paste, it actually improves continuity through the connector pins. You have to be careful with the stuff as it is a conductor, no smearing it all over the place like di electric grease. Each pin has to be coated separately with a toothpick or other suitable tool. I found the stuff at a Model train shop they use it before snapping the tracks together. Stuff seemed to really help, with various sensor (very low voltage) connections and for smearing up grounds after a good cleaning.

Click to expand...

With todays piddly little pin connectors when we suspect a problem , we will use a product call stabilant 22 (I think) which is also a contact enhancer. I believe wurth makes it.

i find a set of oxy-fuel torch tip cleaners work decent for cleaning the female portions of a connector. i use that when just electrical cleaner isnt enough. they are small enough to get into the part.

I re did all my ground wires last summer. Im gonna check ouch the B Latch relay Socket or Shock tower whatever its called.

When you take it out, do you do so with your Jeep running at the time or shut down? If you take the intake boot off, you can look down in the hole and see the pintle.

Did you trying swapping the other relays around?

I turn the jeep off, then pull the relay and it will start up fine. I just took the wires out of the relay socket and cleaned them, They looked looked good. Still have the same problem its been 2 years and the jeep is an 87 so im not gonna spend anymore time on this problem. Unless someone comes up with an idea i haven't tried yet. Should i try greasing up the hole so the pintle goes through easier? Yes i tried swaping the relays and even used new ones.

Just for the heck of it, stick a volt meter lead into the 30 pin for the B+latch relay to a good chassis ground (then the ground at the dipstick holder, then a battery ground). See how close you are to battery voltage. Then measure the voltage with the motor turning over (while cranking).
If it is in fact reving to 3000 and staying there and it is anything to do with IAC, really only a couple of things are likely, low voltage to the IAC or the IAC is sticking.
Most times the IAC sticks it is the gear drive for the pintle, a shot of spray oil towards the rear of the pintle (stopper or piston), so it runs behind, thins the grease and loosens the junk up. The well and seat fro the pintle, needs to be ragged out, I use spray oil and Q-tips.
I'm pretty sure the B+ latch relay 30 pin and the ECU share the same splice for power. This might narrow it down for you, too whether it is a voltage problem or a component problem.
Most all of the sensors share the same ground with the ECU (except the four pole TPS connection and a few others), A good place to test your grounds is to ohm the ground at the three pin TPS connector. Test the ohms between the TPS, three pole connector and chassis ground, see how near it gets to zero ohms. The higher the resistance, the worse the ground circuit.
I've had more successes, troubleshooting the wiring (splices and connectors) than I have swapping out components.

Most of my problems were c101. Twice I had the car stall due to number 6 fuel injector stuck open, gushing fuel into the engine, the second time so much fuel that the engine hydro locked. I thought I had a broken spring in the injector, so I replaced it. A few days later, same problem. Replaced the injector with an other injector, same problem. After taking the spark plugs out and blowing the fuel out of the hydro locked engine, I wigled the c101 connector and the car started up and ran perfectly. Since bypassing the c101 connector a year ago, it hasn't skipped a beat, and coincedentley, the idle flare on start up has gone away.

Ron Hyslop said:

Most of my problems were c101. Twice I had the car stall due to number 6 fuel injector stuck open, gushing fuel into the engine, the second time so much fuel that the engine hydro locked. I thought I had a broken spring in the injector, so I replaced it. A few days later, same problem. Replaced the injector with an other injector, same problem. After taking the spark plugs out and blowing the fuel out of the hydro locked engine, I wigled the c101 connector and the car started up and ran perfectly. Since bypassing the C101 connector a year ago, it hasn't skipped a beat, and coincedentley, the idle flare on start up has gone away.

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I bypassed more than a few of the sensor wires around the C 101, I'll eventually get around to doing the rest. I had multiple voltage loses and excessive ground resistance going through that sucker.
There is a ground splice about four inches inside the harness after the injector harness makes the bend at the firewall. My ground splice squeeze connector was hardly squeezed shut and the wires were just kind of laying in there. I was amazed it ran for 15 years that way and didn't crap out at every bump.
There is also supposed to be a red wire splice for the relay block, that more than a few people have had issues with.