Chosen Solution
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.
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.
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!
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!
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.
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.
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! Update 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!
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
I have a 2003 hyundai elantra, first was fine then all of a sudden my car rpm would go high when in park or low and sometimes turn over idling withe my foot in the break, check engine light would come on and off and if I went into a fast food line, if my car Sat it would idling low and stall then turn over, well looked it up and figured IAC valve and check engine light came on and stayed, took it off clean it out and put a can of seafoam in my gas tank, took positive off battery to reset and light came off, day later came back on (getting low gas mileage btw) and after a day or two all was fine except for a high idle but it wouldn’t stall our anymore, it was great to have my car back, until the cold weather kicked in and I go to start my car after a 6 hour work shift and there’s ice even on my windshield, go to start it and it wouldn’t stay on, kept trying figured to start foot had to be pressing gas and continue to do so until it warmed up, still would have VERY rough idle and hasn’t really been driveable with idling problem and sometimes would turn on and sometimes not, well I thought maybe motor in iac was going bad so I ordered a new one and put it on, reset battery again so check engine light was off, drove for 2 minutes with it great then after that check engine light flashed on, not back on yet but having the same problem wheb idiling slow (turning into my garage) turns over and stops, have to put in park and turn key again, keeps doing it, any ideas on what it could be I’m dying for help, I’m a 17 year old working and can’t afford a shop and I need my car for my job
Hey guys I’m having a p0123 code replace the tps its not that runs really rough a 2000 rpms and it stalls after giving it gas it gets horrible gas mileage but also my signal wire is getting 5 volts at the tps plug I cant find the issue
