Idle air problem. no pcm output?

My '98 Cherokee with a 4.0L pitched a p0505 code. replaced the IAC and now it wants to idle at 1500-2000 rpm. Still has a check engine light. Reset instruction said drive it above 40 mph for at least 5 minutes. I did that and still has the code and idles high. Checked the circuits from the IAC to the PCM and didn't find any opens or shorts. I'm thinking the PCM isn't sending the signal to close the IAC or i got a crappy IAC from autozone, but probably good based on the ohms readings I got. I checked the ohms on the old and new IAC which came out about 5 ohms difference. 47 vs 52. I'm looking for any advice before I take it in and have a shop look at the Jeep. I do not want to have to replace the PCM. Any help would be greatly appreciated.

lsjjn5 said:

. I got a crappy IAC from autozone.

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Asked and answered. Buy genuine Jeep OBD engine sensors. PCM failure is very highly unlikely.



Inspect the wire harness for corroded/damaged wire connector pins. Is the Throttle Body and IAC cavity squeaky clean ?

P0505 - Idle Control System Malfunction

Possible causes

- Faulty Idle Control System motor
- Idle Control System motor harness is open or shorted
- Idle Control System motor circuit poor electrical connection
- Vaccum leaks or damaged hoses or improper routing

Update: I went ahead and replaced the IAC with genuine Jeep and it didn't fix the problem. I took the Jeep to the dealer and the say the PCM is not putting out a signal on the IAC circuit. So as my luck would have it, I'm replacing the most expensive part. FML.

No issues with the wire harness or the IAC plug ? Tested/inspected for melted wire insulation, corrosion, failed wire splices ?

After exhausting all the logical and cheaper possibilities, one might consider a good used PCM.

I checked the wiring. No faults. Dealer confirmed the wiring is fine. The pcm is bad. Now I need to find one. Junkyards near me don't have them. Any ideas where I can get one?

all over ebay preprogrammed, or check car-parts dot com. But then dealer has to reprogram, was just looking at this on my WJ.

A used ECM is $19 at the local Pic-n-Pull, and the warranty is $6. Most people find that the refurbished ECM's have poor workmanship and questionable quality control.

around here the dealer then charges 116 bux to reprogram for the correct vehicle.

1997-2001, if the ECM donor is the same as the recipient (year/engine/trans), re-programming is not required.

mine is an 03 WJ

Tim_MN said:

1997-2001, if the ECM donor is the same as the recipient (year/engine/trans), re-programming is not required.

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You can't forget about emissions (Fed vs CA). Also if you have SKIM it will need to be reprogrammed. So in a nutshell, if you find an ECU with the same part number as your current ECU it will work just fine without programming barring you dont have SKIM.