Cleared codes, suddenly high idle.
 

96 XJ AT: I had my check engine light come on, problem was misfiring due to contaminated fuel. New tank, changed out pump assy/filter, added lucas fuel system cleaner to tank and it ran great. My check engine light was still on tho so shut it down and left the neg batt post dc'd for an hour or so, and when I reconnected it and restarted it, still runs great, light off, but idles around 2500 rpm or so, even after driving it for half an hour. Very strange, checked for vac leaks with starting fluid, none at all. TPS is new, iac was recently cleaned along with valve body/airflow sensor. I've never had any issues with idle on this thing, now suddenly the engine's racing and the only thing tween good idle and bad was dc of the batt. Any ideas??? Thanks

After clearing the PCM's memory it does take a few trips for the PCM to relearn the IAC settings.


If it doesn't relearn look for a vacuum leak on the intake manifold hose connections.

Ok, maybe I'm being impatient, will drive it a bit more. Thanks, I was about to go look for parts in the picky pull :stuart:

Make sure you look over the vacuum lines off the intake.

Thanks CCKen, I blew starting fluid every which way and didn't phase it. I'm starting to suspect something very coincidental might have happened? I'm tossing a AIC valve code, so picked one up. I'm an unrepentant parts swapper I guess, well I did spec the TPS, and it was .9 and 4.1 and smooth, not sure if that's enough to mess things up or not. Much appreciated, will post results.

Wow, no luck, didn't change a thing. It's running at at least 3k rpm. Tried the starting fluid again, no reaction. What the heck? Is the pcm possibly at fault? Nothing was touched between resetting the computer and the idle situation, not sure where to go from here.

Now getting codes 25 (IAC/wiring) and 42 (automatic shut down relay). May be premature but I get the feeling my engine computer isn't feeling well. Btw my tps wiring tests normally, so far I haven't found any info on how to test the wires to the iac.

Pull the intake boot off the TB and see if the throttle plate is closed. There will be a mall gap between the TB and the plate from the stop crew holding open (don't try to adjust this screw). If the plate seems to be held open remove the cruise control cable and throttle valve cable and see if the plate closes. If no change, try pushing the throttle arm to full closed.


I don't have test procedures for the IAC operation from the PCM, only static resistance reading for the IAC stepper motor. But, you have a new IAC installed so I think you wouldn't need to do these tests
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Yes, thank you, I took the boot off and started it, even, and it's running that fast with the plate closed solid. A whole lot of air coming thru that little rectangular iac port making a "heck of a racket" (?) I love colloquialisms. Hard to imagine that much air could come thru that little iac port if it's actually doing it's job? Suppose I should just take the iac out and make sure it's actually moving as it should be.

Did you remove the TB and make sure there's no crap in the IAC pintle orifice that would hold the pintle back/open. Seal on the IAC, right?

Valve did come with new seal, just dc'd the TB and removed iac looks clean in there and can blow through it. I also plugged in the iac valve with the key on, expecting it to move and not much happened at all. I can hear it click click a bit once in a while but it's not moving. Problem??? Not exactly clear what's supposed to happen there, thanks again.

Latest, picked up a used pcm, stuck it in and it still wanted to rev up. So replaced it with the old one and it's idling semi-normally now. Bit high maybe but much better. No idea, intermittent wiring issue, or spirit possession.