huntingman2706217

lol... the whole point of posting in a forum is to get an idea of what it might be and fixing it themselves... without taking it to a costly mech somewhere... lol

june dog

MIne does the same thing.On the front of the throttle body take off the cover by the throttle positioning senor. it will look like a plunger ,clean it with carb cleaner and spray it with wd/40.reinstall that should take care of your fast idle.For some reason it gets dirty easy simple fix.

finneys98xj

Replace the PVC Valve that maybe stopped up and causing some of your problem

wildmustard

Started fine, idle speed crept up as the Jeep warmed up. Topping out near 2000 rpm. Looked at and replaced tps. Same. All vacuum lines checked out, no issues. Also had the usual cracked manifold at the collector. E-bay a new, old stock item from somewhere. Then replace. Easy enough job actually, though a ratcheting box end 14 mm wrench for the underside bolts is a must-have. Make sure you have replacement injector o-rings and conditioner (special grease, even vaseline). Magic! Perfect idle. And quieter and a whole lot safer. 1993 4.0. A couple of'only in Canada' mods. Otherwise stock.

cruiser54

Old thread. Common problem.

Go to www.cruiser 54.com and do Tips 1,3,4, and 5 first. Your TPS and/or it's grounding system is likely wonky.

xjnm

Isn't wd-40 bad for the sensor? If it's not I will try this because I cleaned mine and it helped a little bit but still not totally fixed.

cruiser54

Yes it is. Fix it right using my Tips.....

Caish

Renix are notorious for ground issues.
Clean the grounds at the dispstick.
on a side note occasinally mine will idle fast like that, I cycle the key three or four times and it tends to reset the IAC and idles fine.
There is a relay, back one if i remember right, was just reading the FSM and Renix manual it stays energized for 3 to 5 seconds after key is off to give the ECM time to reset the IAC for the next start.
Make sure its good too.

xjnm

I don't have rennix, will they still apply?

cruiser54

The dipstick tube grounds, yes.

wildmustard

Yes Cruiser, the TPS problem is well documented. I just wanted to point out that in my case the cracked exhaust manifold was very likely the problem. Unless I coincidently bumped a ground or some other part or connection during the manifold repair, replacing the cracked exhaust manifold resolved the fast idle problem. This was after chasing most of the other analysis and repair suggestions without a resolution.

cruiser54

Not likely the exhaust manifold itself had anything to do with it.

I've never experienced that or heard of it.

96Nasty

I had this issue and it was because of my exhaust/intake manifold. there was a bolt sheered off in the head. take your manifolds off and replace the gasket. when they're off, check the bolts and the thread holes to make sure they all check out. this will cause a massive vacuum leak.

cruiser54

Here's a thought....

How about diagnosing whether or not it's leaking there first?

Easily done with a can of carb cleaner.

96Nasty