TapouT

My Jeep has been doing this ever since I bought it back in May of this year. It's a 1989 Jeep Cherokee Pioneer with the 4.0(142,1XX) miles, AW4 Transmission and it's 4X4. Here's what it does...Sometimes when I start it it'll idle wide open like 2500-3000rpm's. I have to shut it off and wait about 10-15 seconds and start it again. It usually takes 1 to 2 times of restarting it to get it to idle back down. Also, when coming to a stop or letting off the gas while driving it starts idling real low and when coming to a stop I have to put it in neutral and rev it up to keep it from stalling. When I put it in neutral and rev it up it idles fine but when I put it in gear the Jeep will jump then fall on its face and idle super low to the point of stalling(this sucks in drive-thru's!!). Then when I drive to give it gas it hesitates for about 1-3 seconds before it'll move. If I don't give it enough gas or if I have to stop it'll shut off...

Example: If I'm at a 4-way intersection and I pull up to a stop sign and there are other cars and they flag me down to go I'll go to give it gas but my Jeep takes a second to get going because it surges and if another car jumps out in front of me to go first and I have to suddenly let off the gas it will stall out.

If I'm out and about and it starts idling real high I usually just pull into a parking lot and spray some carb cleaner in the throttle body with the Jeep off and then start it back up and it idles perfectly fine for awhile unless it shuts off again but I usually pop it in neutral and rev it up before is stalls. Why would spraying carb cleaner in the throttle body make it idle like it's supposed to?

It usually does the high idle thing after it stalls out but not all the time. I've cleaned the Idle Air Control Valve, cleaned the throttle body, put a brand new air filter in, gutted the cat(it was rattling badly) and I just don't know what's causing this. It also likes doing these things when the Jeep is hot so I'm not sure what that could be but it will also do it when first starting/driving the Jeep for the first time of the day so I'm not sure...PLEASE HELP!! I know there are some Jeep/Renix whizze's out there that can help me fix this bug! ANY and ALL help is VERY MUCH APPRECIATED!! Thank you!!

captainwoot

Hi , is your jeep equipped with an EGR vavle, sometimesthese can malfunction, causing an vacuum leak at the intake manifold, this will really mess it up. or posssibly your idle seep motor in not working correctly.

TapouT

I'm not sure if my Jeep has an egr valve although I'm sure it does. Where is it located? If it's malfunctioning I'll just plug it. I doubt that it's the Idle Air Control because I unplugged it while the Jeep was sitting at idle and it didn't really do much it just made it idle a lot lower to the point of almost shutting off.

builtnotbought89'

100% sure ur idle prob. Is ur throtle position sensor! Take ur throtle body apart & clean the hell outta it, & then readjust it! If it still idles high on start up replace the sensor! Search "TPS" on our forum! I'd also replace the O2 sensors just cause it will help u on start up!!!

TapouT

What should I do? Get some electrical parts cleaner and clean the sensor itself and where it plugs in at? Do you think that will help? Thanks!

builtnotbought89'

Ya but I would just take the whole throtle body off & clean the hole thing with just carb cleaner!!!
That's all I did when I had that prob. Then just readjusted it (while running) to set the idle where i wanted it!
Idles fine ever sence! Total it will only take u an hour or so!
Good luck bro!

TapouT

What all is involved with taking the throttle body off? I don't see any bolts holding it down lol. I've never taken it off before when spraying carb cleaner in it I just pulled the inlet tube off and sprayed it through there. Sorry about all the questions and thanks for the help!

builtnotbought89'

No worries! If u take off the air filter tube off there is 3 torqes head bolts in there holding it down! Then the TPS is the sensor on the right! After u put it back together with the inlet hose off, & the left sensor reinstalled start the bolts for the TPS & reconect it! (This way u can adjust the TPS)
Now start the truck & I think twisting it all the way counter clockwise is lowest idle! Figure out where u want ur idle, then tighten it down!
Let me know how it goes!!!

XJ_SPORT

it could be the fuel pressure regulator too

builtnotbought89'

True! If you have the money I'd replace the pump & fuel filter as well! & what dd u mean u "gutted" the cat? the cat.s cohm was braking apart & u took it all out???
I'd replace the cat also but that's a bit more spendy! first let's get ur TPS high idle issue straitened out!

TapouT

Yeah the honey comb was messed and broken up pretty bad so I took the muffler off and busted the comb up and turned the Jeep on and let it run all of it out. There isn't a single piece left in there now so I basically don't have a cat lol. I feel so stupid because I've pulled the inlet tube off plenty of times to spray carb cleaner in the throttle body and I've seen the torx bolts holding it down Do you have any idea what size they are? I'll go ahead and do that tomorrow when I have some free time.

builtnotbought89'

I don't off the top of my head! Sorry

4wheeldrivenewbie

one quick ques wouldent a leaky exhaust before the cat cause some of that rough idle and start maybe bogg out cuz i belive i have a leak its some where between the cat and the manifold and my car runs like you discribe maybe throwing off a sensor or adding extra buildup on sensors of some sort

4wheeldrivenewbie

well i hate to tell you guys that the tps bolts will prolly snap due to age and being frozen i already snapped one of my bolts i however dident preoil them well i also sprayed alil carb cleaner on and around tps and it dident seem to do anything. also builtnotbought what would lead u to belive this sensor and that one is bad i as i donot see any idiot lights on sept my brake light or are there no idiot lights for the tps and o2 sensor i would think there is if so i dont have a light on but i am hopfull replacing both sensors u mentioned would resolve my prob but dont wanna spend extra i do no this there was a recall for the 89-90 jeep 4.0 tps which would cause sometimes high startup idle cause the car to just wanna go without touching any gas

4wheeldrivenewbie

did u ever fix this problem i never did i pulled out the iac and noticed some carbon blk gunk on it so i cleaned it off with some brake cleaner and it was all shiney i also sprayed inside the sensor holes till i barley saw black in the cleaner was almost clear and put it back on started it nothing it still stalled out in drive and when i started it it idled at 2000 but dropped down almost right off where as before it stayed sometimes for 5 mins id have to shut it off