2000 xj idle problem

This problem normally happens more when it is cold outside but does happen during the summer as well. Its a 2000 xj with 4.0 in it and when you go to start it up in the morning to let it warm up you have to sit with your foot on the pedal to keep the rpm's up so that it will stay running. Usually it takes a couple of times to get it started as well. Won't start on the first try. Every once in a while i can get it to stay running with my foot off the gas but when i come back outside to leave it has died.

Also i am getting some weird low idle problems. There are days where it will sit and idle in the driveway at around 400-500 rpms. Don't know how it does it but it does.

Need some help with getting this jeep to run a little better. Last winter i went and did a complete tune up on it and put a new tps on it as well as cleaning out the throttle body. Any help would be great.

Thanks,
Ben

Jeepguy91 said:

This problem normally happens more when it is cold outside but does happen during the summer as well. Its a 2000 xj with 4.0 in it and when you go to start it up in the morning to let it warm up you have to sit with your foot on the pedal to keep the rpm's up so that it will stay running. Usually it takes a couple of times to get it started as well. Won't start on the first try. Every once in a while i can get it to stay running with my foot off the gas but when i come back outside to leave it has died.

Also i am getting some weird low idle problems. There are days where it will sit and idle in the driveway at around 400-500 rpms. Don't know how it does it but it does.

Need some help with getting this jeep to run a little better. Last winter i went and did a complete tune up on it and put a new tps on it as well as cleaning out the throttle body. Any help would be great.

Thanks,
Ben

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Have you checked the IAC valve? Any vacuum leaks?

No i have not. What is the best way to check for vacuum leaks?

I'm told you can run an unlit propane torch around the lines. If you hear your engine idle kick up, you've got a leak there. Repair and move on.

It's more than likely the IAC. While a vacuum leak can occur in a 2000, it's not likely the problem. If there was a vacuum leak, any leaks would tend to be at the rubber fittings on the intake manifold and at the cruise control module.

So should I look at replacing the iac then?

Jeepguy91 said:

So should I look at replacing the iac then?

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I'd first clean it gently with throttle body cleaner, reinstall and see what happens. If there is little to no improvement, then replace it with new and see if that helps.

x2 on cleaning the IAC. While I haven't experienced this problem on a 4.0L XJ I had a similar problem on a 5.2L ZJ (similar IAC motor). It would fire then die. If i kept my foot on the pedal to crack the throttle body it would stay running. If I let off it would die. Replaced the IAC and its fine. Cleaning did not help my case.

Definitely clean your IAC....but also check your vacuum line going to your reservoir in the front bumper, passenger side. I have a 2000 also, and mine was so brittle and gone that it would crumble when I touched it. Easy to overlook since it is kind of hidden, but generally if it is bad you will only get air out of the defrost vents.

Jeepguy91 said:

....have to sit with your foot on the pedal to keep the rpm's up so that it will stay running. Usually it takes a couple of times to get it started as well. Won't start on the first try. Every once in a while i can get it to stay running with my foot off the gas but when i come back outside to leave it has died.

Also i am getting some weird low idle problems. ....

Click to expand...

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging.



Your symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will relearn the idle settings after a short period of driving and the engine will start and idle normally.

Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem. Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace them as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body.

If the symptoms reoccur, you need to have your battery and/or the alternator load tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.

Cleaning the Idle Air Controller (IAC), regular tune-ups, and using fuel injector cleaner should be part of your routine preventative maintenance.

Thanks all for the advise on what to try. Will give it all a shot and go from there and see what happens.

Took me 10 minutes of holding my foot on the gas this morning for it to stay running by itself and this is how low in rpm's it was running. Gonna look into a new iac this weekend.
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Just out of curiosity, have you tested your alternator?

Had it tested this past fall and it checked out good

These things do crap out randomly. Do you own a multimeter? It takes me less than a minute to check, and I had to teach myself how to do it. :bawl:

Yes I do own a multimeter

Check out the battery terminals with the engine off and then running. Post up what you find

I'm betting its the IAC. The PCM should re learn the idle very quickly, not 10 minutes. With my stroker it starts right up after the PCM has been cleared and finds the correct idle in a minute. The RPM in the pic isn't abnormal. But the voltage shown on the gauge is quite low.

Legit idle after 20 minutes of operation--fully warmed up--is 700 to 750 RPM. The automatics are checked with the transmission in DRIVE--this should be done with someone's foot on the service brake pedal.

Just out of curiosity, have you tested your alternator recently ?

At idle you should have a minimum of 13.4 volts or more. Your volt gauge is indicating low.