Slow start, erradic idle, but only when warmed up

The kid complained yesterday that the XJ "wasn't driving right again". He's often vague so I had him take the car to school. I get in this morning and it takes about twice as long to start. I start driving and she seems fine. I get about a mile down the road and pull over now that its warm. The idle drops and gets very erratic and I can feel the engine bucking around. Kind of like my mom's old station wagon did when it dieseled.

Also, while it idled erratically, the throttle position didn't make a difference.

It does this for a couple minutes and then dies. I crank it for a good 20 seconds before it catches and then idles the same for about a minute until the engine roars to 2k. I quickly pop it in drive and head home. It drives nice until I pull onto my street and let it come to a full stop idle. BAM, it does it again.

I left it until cool and she fired up and drove the rest of the way up the street just fine and idled like a kitten in the driveway.

Any thoughts?
I had pulled the throttle body and cleaned out the IACV about a month ago when it had some idle roughness but she's been fine since. Is there a test for the IACV?

Thanks for any help you can give me. It's warm and i'm itching to get up into the mountains!

and the year is? and 4.0?

winterbeater said:

and the year is? and 4.0?

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It's a '93 with a 4.0.

Assuming that you have had no check engine light/ checked codes for clues?? You can do that with the key-on, key-off technique for a 93. Might be worth it to give that a try.....

Always review tuneup hardware when symptomatic. Might be something else but don't want to chase your tail. Plugs, wires, cap, rotor, fuel filter for your 93.

Cap and rotor are new, wires about 20k ago, probably could use a fuel filter but the pressure was a solid 32psi @ idle and with pedal held to 3k. The clock is sitting @ 130k, I've put 30k on it and don't have a clue when/if the filter has ever been changed.

Any sensors that would cause this? Can I test my IACV?

No test for the IAC outside of the dealership--they have a tool to "exercise" the IAC.

Is there any difference in the idle if you unplug the IAC?

ok, went out tonight to fire her up and get her warm to test the IACV by unplugging while warm and see if there was a difference. She wouldn't start. Cranked hard and sputtered while trying to start. I knew then it wasn't the IACV and suspected the coil. I had read quite a few post a couple months ago when it first started and was going to change it out but then the battery took a dump after it sat for 3 weeks. Wouldn't hold a charge ever after having it on the charger over night. New battery made the problem go away, for a while.

Anyway, tonight I went and got a new coil and she fired on the first revolution. Faster than I've seen in the 3 years I've had her.

I'm so happy! I love my XJ! And I'm really glad it wasn't a fuel pump!

Thanks for all the advice. This site has helped me more times than I can count. That's why I pay my dues...

smcdonaldaz said:

Thanks for all the advice. This site has helped me more times than I can count. That's why I pay my dues...

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Funny thing is that this time you fixed it on your own! Glad it's working right now.

JJacobs said:

Funny thing is that this time you fixed it on your own! Glad it's working right now.

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Not really on my own, the idea of the coil came from previous research here in the forums. Besides, even if it was on my own, "my own" has come from hanging around here, reading and asking questions. Before I bought my XJ I had never owned a Jeep of any kind. I found this site while researching what kind of off road vehicle I wanted. I lurked for a long time after I decided on an XJ and before I bought one trying to decide which "flavor" of XJ I wanted. I have a '93 Civic I'm building an engine for and I've yet to find a forum where the people are as helpful.

So yeah, I came to the conclusion this time on my own, but I had standing behind me as I did.

Gosh, I just sounded like a evangelist didn't I? Sweet!

smcdonaldaz said:

Gosh, I just sounded like a evangelist didn't I? Sweet!

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Amen.