Hey Jeepsters
I have a really crazy problem with my 96 cherokee automatic idling low. I have changed the air idle control, TPS,Both oxy sensors, new battery,Plugs, wires, cap rotor, new battery/gnd cables,new cat & exhaust ,cleaned and checked throttle body, no vaccum leaks ican detect,charging good. I do have a crack inthe exhaust manifold dealer tells me but not bad. checked map sensor ok I think but did not change. Jeep will start up and idle fine (750)when cold but after driving for 10-20 minutes the idle drops to 250-200 at stoplights. or under and sometimes stalls at stoplights. When stalls Starts right back up. Weird thing to me and very telling is if I disconnect neg cable for a few minutes. Jeep will idle fine for a day but next day low idle problem will return. Jeep runs great and good power & oil pressure. I am at my wits end and this is my wifes daily driver and shes gonna get rearended I gotta get this fixed. I am pretty good backyard mechanic but this one is tough. Anybody got any ideas or experiences? Any help much appreciated

 

You mentioned the negative terminal, this may not be your problem, but it never hurts to check all the engine grounds. Clean the terminal on the battery really good, the strap from fire wall to the cylinder head is uaually suspect at best most replace this with a #4 or #2 AWG wire, and near the oil dipstick tube, and coil, the last two, usually require degreasing, then sanding scraping to ensure good contact. Bad grounds have been found to be the root of a many odd issues. Like I said, may not be the cause of your problem, but its just a little time investment, and one more thing to rule out. Even though they have been replaced the IAC/TPS could be still in play here. Use the search, the is a procedure for testing the TPS, you will need an analog Volt Meter. Good Luck.

 

Did you check your o2 sensor wires? I have a video showing my jeep doing what you described (its a 2000 but should be similar)
http://www.youtube.com/watch?v=USufL...4&feature=plcp

The problem turned out to be that my o2 sensor wires had been rubbing on my driveshaft and blew my fuse. Check your o2 sensor fuse also.

 

Tylerspyler The sensor wires all looked good and not rubbing when I replaced sensors But I will check again. Where is the sensor fuse located. BTW this thing is not throwing any codes except a neutral safety switch code which I think is unrelated Thanks

Fishtaconc I replaced all the main leads and grnd wires cept the firewall cos with#4 cos Its a ***** to get to the cyl head bolt. Gonna need a angled socket or something to get to that I have put 2 IAC's and 2 TPS's in this thing

Thanks

Any other suggestions would be greatly appreciated! Trying to keep my sanity!

 

had problem like that once. bad fuel. might check fuel rail pressure.

 

My 2000 had it in the under hood fuse panel. Just test all the fuses with either a test light, or use a multimeter, or take each one out and inspect it. Mine blew very violently and almost melted the fuse itself. Other than that, all that is really left is to reset or replace the PCM. but that is big $$$.

 

It's not normally suppose to be messed with, but in at least one thread the guy's answer was the stop for the butterfly on the TB. (whatever it's called today). The plug can be hit off center with a punch and removed to get to the adjustment, or one guy just bent the stop a tad. Was me, I might experiment with a shim there just to see what that does.
So you have real good power? Wonder if a restricted exhaust can be ruled out.
Codes?

Just on GP, I might go around with short little bursts of starting fluid looking for vacuum leaks. If you hit one the engine sound will change.

 

DFlint Thanks for input. I have new cat and exhaust Here's the puzzler and all techs reading this pls consider... When I disconnect neg cable for 10 mins,and that RESETs the pcm and I fire it back up the jeep will idle fine at 750 for about a day then problem returns. I know that after reset pcm operates in closed loop (Uses pcm presets) till temp comes up and the goes to open loop (pcm sarts reading sensor info) So I am thinking of disconnecting my oxy sensors to test and see if makes a diff TYspy had a similar prob but he was blowing fuses.
Anthing wrong with disconnecting sensors temporarily How should enginge run? Any and all input appreciated here Thanks BTW only codes it shows is a neutral safety switch I don't think that is related

 

"'disconnect neg cable"". yea, I did get that. Just that so much is inter-related I never know for sure what affects what. For instance, if my NSS is telling the PCM I'm in neutral, when I'm actually in drive, Idk what would happen. Does it start in gear? I might get that code cleaned up, just to be sure it's not muddling the issue. Here's a link with some of it's secrets. http://bc4x4.com/tech/2010/jeep-neut...ty-switch-nss/ Well, darn. That one doesn't have the "Pin out" or whatever. It's a busy little bugger anyway.
I'm no help on your 02's except that the rear only monitors the cat. Also some say a reset takes overnight "for the capacitors to bleed off". Then you might expect it to take a good number of hot/cold cycles to relearn. 40 get's mentioned. I would think you might want to get the NSS straight anyway...Also, even with all that brainy stuff going on, that idle stop still needs to be within some parameter. (bringing it up might not necessarily mean it goes too high)
Like tyler points out, there are fuses for the 02 heaters, and relays as well. Certainly would want to check the fuses and at least jiggle, unplug, replug the relays. There should be a code though. Also allot of us have added an engine to chassis ground since Jeep didn't over do it. (mine is from the AC compressor to a Rad bolt, dipstick tube mount to below the shock mount is better)
Hopefully freedgr or tj can chime in as well. I'm just learning here.

 

The NSS is just needing a cleaning I think. This is an auto and starts fine in park. I am hoping somone can tell me how the engine will run with both oxy sensors unplugged for testing. I am thinking I may have a one (tho both are new) I also will check the hell out of the vacc lines Just cant put together in my mind why it runs good for a day and then problem returns. Ist guy who helps me get to the bottom gets a check in the mail or VISA This jeep is great cept this problem is beating me up. THanks again Any more ideas out there?

 

Just wondering, did you install the TPS right? I dont even know if it is possible to put it in wrong. Have you tested it with a multimeter. should use a scantool and see if the computer reads it. My normal readings are 17.1% at idle and 76.9% at WOT with a scantool. They are all i little different but should not be 0% or 100% at idle.

Also, have you tried running it with and without defrost/AC on? I know most vehicles (jeeps especialy) idle up a little in order to keep proper pressure in the airconditioner hoses.

Just an idea, when you start it in the morning, when it idles right, unplug the iac while the engine is running. (will throw a code) Drive it around and see if it improves or gets worse in the same conditions as before. It may run a little on the rich side due to the iac not retracting. I do not know if the jeeps do this or just have a preset position.