Idle Question

[jonbeling]

My jeep is having a problem idling. First, half the time the car wont turn over unless I press the gas as im starting the engine. Then if I let go of the gas it will just shut off and wont idle at the proper rpm`s. However after doing that about 2 times it finally will turn over with no problem. Its been going on for about a month now. Im not sure if this could be related to my oxygen sensors in the vehicle??? Anyway and help would be awesome

[Accumulator]

I dunno a *thing* about Jeeps :o but if it`s the O2 sensors I`d expect it to throw a CEL (check engine light). If that happens you oughta be able to pull a fault code (you have OBDII, right?) that will give you a starting point. Some autoparts shops will pull codes for you (since they expect you to buy the parts to fix it) and save you the cost of a trip to a repair shop/dealer. I somehow doubt that it`s the O2s since it apparently runs fine after the start up trouble. If it runs poorly all the time then that woud be different.



Sounds to me like there`s some kind of "fuel delivery while cold" issue with the FI system or maybe the auto choke isn`t working right.

[LouisanaJeeper]

1) clean the throttle body with carb cleaner

2) replace fuel filter and check for fuel leaks at the manifold

3) check fuel pump relays

4) possibly a low battery or bad coil

5) possilby a bad tps



probably not an o2 sensor



is it a 5.2L or 4.0L?

[White95Max]

See if it starts better if you turn the key to ON for a few seconds before starting it to allow the fuel pressure to build up.



That may help the initial startup, but as far as the engine dying after that, I`d say perform the steps listed above.

[Ben Z.]

Originally posted by LouisanaJeeper

1) clean the throttle body with carb cleaner

2) replace fuel filter and check for fuel leaks at the manifold

3) check fuel pump relays

4) possibly a low battery or bad coil

5) possilby a bad tps



probably not an o2 sensor



is it a 5.2L or 4.0L?



Your problem sounds a lot like #5, but the first 2 are easy and free to do. I doubt #3 or #4 are your problem, but it can`t hurt to check. Not sure about jeeps, but some cars have an idle stabilizer valve (ISV) that could also be a likely candidate. Good luck.

[LouisanaJeeper]

the jeep has what is called an IAC, idle air control wich is what partially opens up the throttle to allow airflow at startup and idle



it is on the throttle body

[MorBid]

I would agree on number 5 (Throttle Position Sensor). If you have the shop manual for the Jeep, it should list the procedure fo checking it (fairly simple and only requires a pair of test leads and a voltmeter.



I`m with Accumulator in that if it was your O2 sensor the car would run like sh*t all the time and you`d get a CEL.



My next guess would be fuel delivery or choke.

[Accumulator]

jonbeling- Glad to see you`re getting some good feedback from people familiar with your vehicle. Heh heh, jusding frm what people are suggesting, it sounds like your Jeep isn`t all that different from my mid-`90s Chevies when it comes to this type of trouble.



IMO you oughta get a shop manual for it. Even if you pay somebody to do the work, being able to diagnose it yourself can be of great value. I spent a small fortune (or so it seemed at the time) on a set of factory manuals for my Caprices but they`ve paid for themselves a dozen times over. Stuff like the trouble you`re experiencing can be pretty simple with the right reference materials. You might look on ebay for some used ones.

[Steve530]

Any symptoms noticed at the tailpipe? Like soot or white smoke.



I`m thinking maybe a bad fuel pressure regulator flooding the engine.

[jonbeling]

its a 4.0. No symptoms noticed at the tailpipe. The 97 zj`s dont have fuel filter that is easy to replace, becasue you need to disassemble the tank and stuff like that, so if thats the case i`ll have to bring it to a pro. I have a chilton book so ill have to dig it up and take a look at it. The battery is ok i`ve had it tested. I`ll probably test the tps tomorrow in the morning. For now on i`ll put the car in the ON position before starting it to see if that makes a difference.



Thanks alot for the feedback!! I really appreciate this

[JasonD]

Is it only a problem getting started or does it not want to idle at all even once it`s running?



As Accumulator stated, the O2 sensors would throw a code that would trigger the check engine light, and even if one went bad it wouldn`t cause this problem.



I am leaning toward the TPS because they are extremely finicky and can come and go. The IAC can certainly cause this problem, but usually does it all the time, not just cranking or while it`s cold.



Same thing with the fuel filter, either its clogged or not.

[Bowens99gt]

I`m with LJ on the IAC.....I had the same problem. I took the IAC off, used carb cleaner on it and it worked like a charm.....I know some people that have had to replace the whole unit though.

[Steve530]

After re-reading you original post, I agree it`s probably the device that controls the cold idle.