2001 XJ 170k on the dash. Last year I replaced the iac and tps from autozone. Last month I started having stalling issues so i took it to the shop and they replaced the iac Again. Problem solved. Ran like new . Well a few days ago I started having high ideal again with the check engine light showing P0505 (iac sensor) P0123 (tps sensor) p0108 (map sensor) and p0302 misfire on cylinder 3012. I was like WTH?!?!? Well since all three sensors are still under auto zone lifetime warranty I exchanged them for new ones. I also disconnected the battery for a good 1.5 hours. Well guess what?? The check engine was still there!!!and it still has high idel a lil over 1 rpm!!!! What can it be? Anyone ever experience this before? I read it could be a vacuum leak but how would that explain the codes for a bad Iac and tps????

 

Head to auto zone and have them clear the check engine code. Kinda odd that you'd have a vacuum leak after replacing everything. Unless the PCM still thinks there's a problem (which would explain the check engine light still being on).The idle on my 4.0 fluctuates from time to time. I've changed out the IAC, the MAP sensor, and TPS, and everything was great until I started going wheeling again lol
-Chris

 

On my 90, (no codes/light <91), it turned out to be my plug on the IAC. Had random high idle till I cleaned that well. (because sometimes turning it off and then restarting worked, I could pretty much rule out a vacuum leak) Mine at least, the plug on it faces up so that stuff can get in there....small stuff, hard to see and clean. Contact cleaner blasted in and repeatedly plugging, unplugging seemed to be the solution.

 

Fixed it. One of the The wires on the IAC plug was loose and it kept popping out. The check engine went away!!

 

And the crowd cheers! Well done.

Btw, can't say I know for sure but I gather if you wand to re-set your PCM, disconnected overnight should do it. 6 or 8 hrs for "the capacitors to bleed down"