4.0L WJ Random High Idle

paradisePWoffrd

paradisePWoffrd

Recovering Project Junkie
Joined
Nov 5, 2005
Location
Newton, NC
A collegue of mine has a 2004 Jeep WJ 4.0L 4x4 that has been giving him some issues. Here's what he told me:

- it will randomly rev to 2k+ RPMs on startup.
- It doesnt do it everytime.
- Previously it only seemed to do it first thing in the morning when the engine was cold, now it is not just then.
- It will rev for a minute or so, then return to a normal idle.
- Occasionally it will rev back up when shifting into park
- Doesnt idle or run rough anytime
- Doesnt throw any codes
- Has had multiple shops look at it and change the IAC and check for vacuum leaks. Problem comes back after a few days.
- Lastly had the dealer's "best tech" look at it, they put a "factory" IAC on it. problem came back. Dealer claims they ran a scan of the system showing no issues. Says the issue is PCM or wiring harness.

I told him it could be TPS, but he hasnt tried that yet.

Anyone seen anything like this? Just tired or throwing parts at it, and doesnt want to drop the $1-2k the dealer will want to change PCM/harness if he doesnt have to.
 
I'm not one to E diagnose, but back in my dealer days I replaced hundreds of later model 4.0 TP sensors for the same reason.
It won't set a CEL since nothing is out of spec. What happens is the TP% will be 1-4% at closed idle and the PCM increases idle speed.
BTW- this former dealer "best tech" still gets called by his old dealer to give advice...
 
hey if your close enough i got tons of those sensors...you could probably just have one lol if you came up this way
 
ohh and i have a pcm from a 00 which will work...just unsure about the "options" he has compared to this one but i have a 99 and 00 WJ..both have good computers and ran good before taken apart but i must admit, many jeeps i've dealt with and never really seen PCM issue in these..IAC, TPS, Cam sensor and O2s since it has 4 of em is about the most common problems minus the piston skirts breaking lol
 
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