99 Laredo 4.7 charging/ PCM/ rough idle issue - Jeep Garage - Jeep Forum

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Old 06-02-2016, 07:29 PM
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99 Laredo 4.7 charging/ PCM/ rough idle issue

Electrical issue:


I have a '99 Laredo 4.7 4x4, since it was about a year old it has had a rough idle under about 900 RPM. Back then it went to the dealer several times (multiple dealer reflash tags on the PCM) for this issue, and the dealer could never figure it out....


It has always had a MIL on with codes P0302, random but rare P0141 and P0161 up until a few days ago when I replaced the cam and crank sensors.


It still has a rough idle, but I've been driving it a lot and the MIL hasn't come back on. My concern it that on cold start the starter solenoid rapidly clicks while its turning over (it always starts, just doesn't sound pretty). The voltage at the alternator and battery while running is about 13.7-13.9v, but my code reader is saying 12.6-12.8v at the OBD-II port.


I'm turning towards it always having a bad PCM, but I took it to the dealer and they said it checks out.


Things I've done:


New four hole Ford fuel injectors


Two new coil packs


8 Champion copper plugs


New cam and crank sensors


New battery terminals


New battery


New starter


Cleaned and sanded all block, body, and exhaust grounds


New IAC


TPS is good


Cleaned the throttle body


Checked for vacuum leaks


Compression test came out fine on all 8


Any insight will be greatly appreciated.

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Old 06-03-2016, 12:57 AM
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Re: 99 Laredo 4.7 charging/ PCM/ rough idle issue

Welcome to the garage.
So it is doing this rough idle since 2000?
You have changed and done quite some things already. That the starter solenoid clicks rapidly, could also be caused by the starter relay or even the ignition switch. Does it only click, or is the starter motor rotation laboured as well, as if the power to the starter motor is interrupted? You could swap the starter relay with the horn relay (both in the PDC under the hood) and see if that changes anything.
The starter problem seems to be separate from the rough idle problem. The P0302 code also didnīt return, while it still idles rough?
If you measured the voltage at the battery with a reliable voltmeter, then i would rely more on that reading then the one from the OBDII reader.
The rough idle could eventually be caused by the PCM, but it will be hard to proove that without changing it. But if you drove like this since 2000, i would leave it as it is.
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