Why does my Jeep Idle at 2,500 every other start?

Its been going on for awhile now. I'll fire the jeep up and sometimes if starts up fine but most of the time it idles to 2500 and I either have to shut it off and restart 30 seconds later or it will slowly go down on its own after about 20 or 30 seconds....However when i take of the Latch Relay the jeep starts up fine. I have replaced this relay but it still causes this problem..any tips?

You talk about the latch relay, so I suppose it's a RENIX? Year, engine, stick or auto will help get better info. Clean your IAC?

87 4.0 AW4 I have replaced the IAC 3 times.

Try cleaning out the IAC bore in the TB. It can cause the IAC pintle to bind.

Disconnect the battery.

Unbolt the relay mount and check underneath for corrosion.

sounds like the TPS

I have done all of the above countless times I've replaced the TPS twice also even tried different adjustments.

well then im clueless.

nw-xj-scott said:

well then im clueless.

Click to expand...

x2, not a clue.

correct me if I'm wrong, but doesn't the Renix have thermostatic air control? that will def. cause the idle to be high on a cold start up until the exhaust manifold gets warm enough to close the door...then the idle would drop.

Joshooha said:

correct me if I'm wrong, but doesn't the Renix have thermostatic air control? that will def. cause the idle to be high on a cold start up until the exhaust manifold gets warm enough to close the door...then the idle would drop.

Click to expand...

do you have a crack in your manifold or downpipe?

Joshooha said:

correct me if I'm wrong, but doesn't the Renix have thermostatic air control? that will def. cause the idle to be high on a cold start up until the exhaust manifold gets warm enough to close the door...then the idle would drop.

Click to expand...

Yeah its right at the front of the airbox but i can't seem to find one to replace it with.

As for the crack in the manifold, No but I did tighten some of the bolts and it didn't help.

Well damn. If you can just hit that little door with a hammer and that idle drops that probably the issue....I don't know much about t-stat air though. I just know how it works! haha. Maybe a junk yard replacement?

I had problems of that sort come and go for years with my first Renix, 87. I have found a bunch of things that cause it. I once found that a fixed, working Renix, would start with a very high idle if you had the jeep in Run for several minutes with the engine off (running say the radio, or doing electrical tests), and then go back to normal by just turning the engine off, waiting 10 seconds, then restarting it. In your specific case it could be:

1) Junk in the throttle body sticking the pentle in the IAC to the throttle body as already mentioned.
2) Funky, variable grounds (loose, dirty...), on the TPS, or other sensors.
3) Hot sensor and controller (IAC is a controller part, not a sensor) wires (versus grounds) that have connector problems. C-101 bulk head connector connections that are too loose, or corroded, same goes for fuse box, etc.... C-101 is on the firewall near the Master Cylinder.
4) You have already covered the IAC and TPS.
5) My floor mat can get stuck under the gas peddle and cause a high idle! Talk about random!
6)The Air temp sensor in the Intake manifold can go bad in a way that causes high idles, sometimes randomly. Ask me how I know!
7) And the best one of all, the funnest to trouble shoot,.......but wait for it...........

ALL of the above!:soapbox:

Joshooha said:

Well damn. If you can just hit that little door with a hammer and that idle drops that probably the issue....I don't know much about t-stat air though. I just know how it works! haha. Maybe a junk yard replacement?

Click to expand...

I don't think the Renix T-stat door on the air box can affect idle speed on a Renix. The IAC, when working properly would conteract any effect from that. That door only operates in the cold winter time anyway.

Ecomike said:

I don't think the Renix T-stat door on the air box can affect idle speed on a Renix.

Click to expand...

X2^^ the butterfly being open or closed will not change anything in your idle speed. The air that enters from either port is before any input sensor, so the ECU will regulate idle speed the same with either air supply (when everything else is functioning correctly)

It wouldn't hurt to plug off the vacuum lines to the air control diaphragm and try starting it, however. If the diaphragm were torn or deteriorated, you could create an unregulated vacuum leak that the IAC cannot compensate for effectively-- just a thought.....

Ecomike said:

I don't think the Renix T-stat door on the air box can affect idle speed on a Renix. The IAC, when working properly would conteract any effect from that. That door only operates in the cold winter time anyway.

Click to expand...

Ya that is likely true because that is really what the design was for. I just have worked on the GM's mostly and they acted up whether it was was winter or summer, of course it was worse in the winter. The IAC does make sense though... It could be giving that T-stat air cntrl a false reading correct?

Might try -just look, don't touch!- check that the throttle is fully against the stop prior to each start up (to narrow it down some). That big a RPM should show up some place if it is mechanical. (Something is not resetting properly?)

Good Luck,
Orange

I've read all the above posts but don't see the thing that finally cured my idle issues with my 90. I have a few vacuum leaks and once they were fixed no more fast idle issues. Coincidence..................I think not!!!

Joshooha said:

Ya that is likely true because that is really what the design was for. I just have worked on the GM's mostly and they acted up whether it was was winter or summer, of course it was worse in the winter. The IAC does make sense though... It could be giving that T-stat air cntrl a false reading correct?

Click to expand...

NO. The T-stat air control only moves the air source to the air filter, it has absolutely nothing to with engine idle! I can only change the incoming air source, from a cold source to a hot source. The IAC and TPS are the only two sensors that truly control Idle speed. A change in inlet air temp can affect idle speed if the IAT (MAT) is giving out bad data, but it would be repeatable, like only show up for hot, or cold starts.