So the last few days my idle has been randomly going up to 1,000 rpm, and sometimes bouncing between 1000 and 1400, doesn't matter if it's in gear or not, doesn't happen all the time, doesn't always happen at startup.

Cruise control works on and off as well, thinking the two items may be related...doesn't seem to be a vacuum leak, although I haven't finished tracing all the lines...

Any common items that cause this or to search for in threads specifically?? Again it's a 5.2.

 

It does sound like it could be a vacuum leak. Have you noticed any oil consumption since this started?

 

Besides the leaks all over where I park no, just picked it up a month ago and it's used/leaked a quart in a little over 1200 miles.

My line of thought is a vacuum leak would be more of a constant/predictable rev issue, as it's not going to seal itself up every now and again to run good then not for a little bit, then alright for a few days, ect... It's just weird, was hoping it'd be a common issue I could get some info on before I have time to dig into it.

Too much life and not enough time right now lol...doesn't help I just picked up a solid 00 xj with 100,000 on it with engine issues yesterday either :/ ....can't pass up free stuff.

 

check the grommet on the brake booster, if it has small cracks in it from old age it could cause this as well

 

Throttle position sensor?

 

Idle Air Control Solenoid

 

+1 on the IAC, Mopar throttle body cleaner works really good, don/t force or move the prindle, just remove it gently and clean it and the hole it sits in ,you can damage it pretty easily.

 

May have found a small vac leak for the cruise control, nothing seems amiss for anything else, and it doesn't effect idle, booster grommet looks good.

IAC was in the thought list or tps as well, cleaning the IAC is next on the list, never had one act up like this (always a low rpm issue and stalling), but it did cross my mind as well.

It's nice to have some responses, thank you guys, and I'll update when I get it cleaned and back together (probably will yank the entire TB and clean everything as I'm sure it hasn't been done)

 

My '94 Grand 5.2 did that random high idle thing too. The big plug going to the PCM turned out to be "loose". I would turn it off, push that big plug tighter, start her up and go.
To be fair I did the TPS, idle air motor, vacuum checks too. It's just an idea.

 

That's also not a bad idea, I STILL havnt gotten around to messing with it yet lol, it hasn't been acting up much either as of late.

 

There is a TSB for the intake plenum pan gasket.

When this is performed ensure that each plenum pan bolt can be bottomed out in the hole by hand tightening. In my case I ended up chasing the bolt and hole threads to clean 'em up, then they all bottomed out by hand. Use new intake manifold bolts because they stretch when tightened properly.

 

Just to finish this thread off, I had a few small vacuum leaks, fixed those up, and cleaned the TB and IAC, both were nasty.

Also replaced the brake switch by the pedal, cruise works now, and the idle is good, although there are a few dips with it here and there so an IAC is on the list to replace but overall everything seems to be cured.