Hawkman

I've got a 90 XJ Laredo with 155k miles. Runs like a champ. Had a sporadic high idling issue that would always seem to go away within a few seconds. Thought it might have been the IAC after reading this forum, so I replaced it. I even installed a new Crankshaft Position Sensor as I sensed the one in the XJ was going bad.

When it got to the point the idle wouldn't go down, I took it to my friend's shop down the street. He hooks it up to his scanner and tells me the TPS is bad. Cost for him from the local parts store is like $120. I thought the price was crazy as I've seen them for around $50, but for the sake of time I said f*ck it...go ahead and fix it. Didn't fix the problem. Then he says the EGR valve has a leak. So he replaces the EGR. Didn't fix the problem. I forward him some info on how to diagnose for a high idle issue. Suggest it might be the coolant temp sensor. Puts in a new one and the high idle is gone, but now when it starts it doesn't do it's normal startup routine of jumping to 1000k+ RPMs, and settling down. Instead, it'll jump to like 800 RPM, but immediately go down to 300 RPM, and as it warms up it will work to around 600-700 rpm. At 5:30 in the morning when leaving for work and the temps are mid 30s, 300 RPM isn't cutting it. WTF happened here? I bring the XJ in that started fine, but had a high idle, and it comes back to me with a stupid low idle after having all these new parts put on? The throttle body has been cleaned. Can the O2 sensors be causing this? PCV valve? Because that's what the guys are saying are next on their list to replace in hopes of figuring out the low idle startup issue. Any help would be appreciated.

ezab

You should test your Throttle Positioning Sensor.

Hawkman

TPS is new, and was rechecked. Found to be functioning properly and within spec.

ezab

I must have missed the fact that you replaced it already when I read this the first time. Did you check all your vacuum lines for damage?

Hawkman

No worries. Since it started fine when it went in, I was thinking one of the new pieces might have been wrong/bad, so yeah...it's good to double check.

The XJ was hooked up to a vacuum/pressure tester. That's how the EGR leak was found. No leaks now.

ezab

When was your last tune-up? If it has been a while it definitely wouldn't hurt.

Hawkman

Full tune up done 15k miles ago.