The Jeep Cherokee (XJ) is a compact SUV that was manufactured and marketed by Jeep from 1997 to 2001. Sharing the name of the original full-size SJ model, but without a traditional body-on-frame chassis, the XJ instead featured a light-weight unibody design.

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Won't Idle Correctly After Attempted Repair-What Next

I have a 2000 Jeep Cherokee 4.0L ( XJ ) limited trim. It will not idle correctly. below the regular RPM or above..... i replaced the idle position sensor and had the IAC system reset by a friend who is a mechanic. ( idle sensor was to blame, to keep my question short). Everything seemed to be quite fine having done this yesterday. Even seemed to run better/stronger.

Until this mourning when it would not idle at all.... until i started and held the gas down above idle speed for about 60seconds. Also does not idle at a consistent speed and occasionally idles rough.

I will be doing a tune up over the weekend since it is due, which is fairly easy with no plug wires etc just the ignition pack over the plugs.

I am not sure if this will help with my current problem since the computer should correct within reason for any ignition timing if i had bad plugs? yea?

If anyone has any ideas? let me know. If i had a bad part in the ignition system it would throw a code? and the check engine light has yet to come on and everything checked out ok just yesterday.

Answered! View the answer I have this problem too

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The computer not showing a code would make me suspicious of mechanical problems (IE not sensors or wires). A tune up is a good place to start. Replace the spark plugs, if you can clean the fuel injectors you should (Seafoam is AMAZING) and if you are so brave, I would check the valve clearances. You might consider coils too. If none of these maintenance things have been done in a while, it may clear up your problem...if nothing else, it's good maintenance! Let us know what you find.

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You could override the idle controller and set the idle manually via this circuit

https://youtu.be/NrUIs_Jw3RQ

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Also make sure that you check for vacuum leaks. Mist the engine compartment with some WD40 around the vacuum lines and see if the RPM increases, if so you know you have a leak. The other thing to look for is the Throttle Position Sensor (it is located right next to the IAC in the throttle body). When it goes bad it will think the throttle plate is either to closed or to open. Of course, a bad (or going bad) fuel pump can give you the same symptoms as well.

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thank you for the suggestion, if you have a link for the vacuum system for my model year please post it, it would be appreciated.. I have not been able to find this info via google, ( never fixed or looked at the vacuum system for any of the jeeps i have owned). I will have my friend check the other sensor as he has the equipment to do that and i have to go back to his shop anyway for unrelated work to be done. figuring out as much as i can before going to him is nice as he consistently helps me maintain it.

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Brian, download the service manual from here http://www.keepandshare.com/doc/3247284/...

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Success !! The spark plugs where in bad shape, way out of correct gap clearance or whatever the correct term is.... there was another answer posted that is gone?, which did help me as well, pointed out the spark plug and other stuff which was the problem...... SO it now idles a bit high and after warming up fairly normal, however i can figure such a minor thing later if i need to having only done this a few hrs ago....... large difference in performance as well of course. I bought a "nice" brand and quality plug this time so it should last awhile before i have to do that again...... it was fairly easy with the help of a friend to hold things and move things out of the way, coolant system hose etc..... Four 13mm bolts for the ignition pack thing....... and then all the plugs.......... put the ignition pack back on taking care to do it all of this correctly as a mistake can be quite nasty to fix. Took about an hour. Having all the correct tools acquired over time helped. I have a K&N filter which is still clean.

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OK. this didn't exactly fix the problem, i should have mentioned before now....... sometimes i have to hold the gas down to start it .........while it runs better of course, once it warms up it still idles poorly / barely. Usually when cold started for the first time of the day it idles a bit high but normal, once it gets to normal operating temp driving with both feet again..... I have read online about cleaning out the throttle body and a weak battery (my battery is old and weak). I have been looking around for a solution and before taking the throttle body off and cleaning it thought i would ask for more ideas. Getting cold out and would like to get this sorted out rather then doing work that won't fix the problem. .... not sure if it matters but the coolant level is fine, the hoses on the top of the engine thou, feel too soft as if not enough pressure or liquid is present. I never did check for vacuum leaks since the problem is not constant and i don't know where the vacuum lines are.

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Another thing to check, if your truck has it, is your IAC (idle air controller). My truck actually decided to spring the same problem you're having (though I have an engine light on). It was running super rough (I could even feel a cylinder misfiring) and didn't like starting. I swapped the plugs and used fuel system cleaner and it runs almost perfect now. It just doesnt like idling when cold. (Sound somewhat similar to yours?)

I've been told that the IAC can be the cause of this. If the truck runs fine except for your idle, check the IAC...that's my next step!

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Thank you for the posting,I replaced the IAC sensor it was one of the first things i did, however it was a used one, i know a bit odd using a previously used IAC sensor, however it came with several expensive parts I needed for very cheap locally ( these other parts work fine). After installing the sensor friend of mine reset the IAC system with his fancy computer thing, it ran fine for the rest of the day then back to problems ( this is before the tune up above i thought fixed the problem without waiting more then a day to make sure)....... i can go ahead and oder a new IAC sensor, just not convinced that is the problem... ( since the same problem exists just a bit different now)....... As far as i know the diagnostic machine was not able to increase RPM's which lead to the diagnosis of the IAC sensor ( This friend is very skilled figuring out problems for family members other repair places could not). He did clean out something in the throttle body awhile ago before this problem got worse.......

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OK, I'll throw my 2 quid in! If your tech friend has a DRBII (Factory scan tool) have him do a minimum air flow test-I'll bet you some (whatever you eat for breakfast where you are)) that it'll FAIL! Good news, all you need to do is an induction/fuel injection service. Don't waste your money with junk from the parts store-use a 2901 kit from BG. One can through the fuel rail, one through the induction system (not a vacuum port-a fogger please), and some 44K in the tank. make sure when you put the tank additive in that you fill the tank and drive that first tank down as far as possible. the longer it stays in at that treat ratio, the better clean up it will do. And yeah, I'd check the vacuum circuits too, but you're probably gonna find the PCV system hoses clogged or broken. Please save yourself some misery and don't use regular tubing-go buy the factory PCV harness. Look at the small one that runs to the back of the engine-it may look fine, but it also may be clogged up with goop. Yes,GOOP! Also becareful with the grommets, they mat be brittle! Good luck!

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I have a 99 cherokee sport straigh 6 4.0L 4X4 standard gear, and i was experiencing similar problems as you. During a year, I took off the fuel tank, cleaned the micronic filter inside of it, cleaned the injectors, changed spark plugs and cables, and everytime i changed or cleaned something, started to work better for a while, and then again, the problem. a Few months ago, a mechanical told me it was the TPS, so he replaced it and reconfigure the computer, so the engine felt very good (stronger), but a few weeks later, it began to give me trouble starting, i had to push all the gas pedal and give a lot of start. So, i had to reset the ECU and the engine began to start right, but the iddle and acceleration problem came to again. The last thing i did was to clean the IAC valve and amazingly the engine began to work fine, i thought all my problems were gone, but a month later the ptoblem started again. i cleaned the IAC valve again, but the problem just got worse, after a few minutes of not running good the engine would not responde to the accelerator pedal. i had to stop the engine, wait for about 30 seconds and then start it again and that would give me another few minutes. I thought i messed it up in the last cleaning to the IAC valve and wanted to replace it, but i read your article and a person was suggesting you to check your vacuum lines. so i checked mine, cleaned one by one, and in the vacuum hose that goes on the rear (next to the cabin) the hose has a plastic device that is supposed to allow air to go just on one side, but mine was dirty and it was allowing the air to go on both sides. Some carb cleanner, and a Little shake were enough to make it work properly. i reconnected everything, started the engine, and HALELUYAH!!!! my engine was working great!!!! i went for a test drive, and i hadn´t felt the engine so smooth for more tan a year. So if you are still having some issues with your iddle, PLEAS CHECK YOUR VACUUM HOSES, SPECIALY THE LAST ON THE REAR, AND CLEAN THAT TINY PLASTIC DEVICE (stil don´t know its name) i hope this can help you too.

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Does your vehicle use a vacuum-operated automatic choke? Rarely, they get sticky and either get stuck full-throttle, or don't quite travel far enough to the proper run positon after their time delay.

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Many mechanical devices on these engines throw a diagnostic code, the IAC is one of them.I just replaced one on my 4.0 engine, it was stuck and did not operate smoothly! It's a stepper motor running a lead screw to adjust mixture, I had the same symptoms you are having now!

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The Mapp and air temp sensor do not throw codes either. Iac doesn't throw code. Straight from 1994 factory service manual! You can monitor with good diagnostic scanners!

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2000 model year is OBD 2 & you can do a min air flow test. The IAC motors usually get stuck because of carbon deposits, they don't go bad often so they can be cleaned rather than replaced. The K&N air filters have destroyed more MAFS be sure its sealed properly and not over oiled. There are cleaners specially designed for this. If the MAF has 4 wires it's heated, make sure the wires in it are cool to the touch before spraying it with the cleaner. Avoid getting the cleaner into the any electrical parts except the two "cross hair wires" in the air stream The throttle body does NOT have to be removed to clean it. In fact if you use the BG induction system cleaner (#206) you'll also clean the IAC at the same time. It does require special tools and training to do properly, but you could try a can of BG throttle body cleaner (#406) or the MOPAR stuff-either will work well, the drawback is you cant get a thorough cleaning of the entire induction system and will have to remove the IAC & manually clean it.

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Same issue except it only happens when cold. Many suggestions that it may be the primary computer. The suggestion it to bag it, encompass the computer which is right side forward facing the vehicle from front on a 99 in a garbage bag and surf a hair dryer in it . Run long enough to heat up the computer and allow it the heat all the way though. If all else is cold and it fixes it then the computer is broke.

If not then the more likely and cheap option is air temp sene pick up on manifold. Hmmmmm. Try tomorrow

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