Ok here is the truck
222k miles, new heads, tune-up and TPS at 220k (2k ago)
I just bought this truck, having a problem cant seem to figure it out:
The truck will start and idle fine for a minute or two, then the idle cuts out from 900 and drops to 600, engine revs to 1200 then back down, check engine light comes on.
Now soon as a accelerate for 20 seconds at more than 1/4 throttle or drive anywhere the service engine light goes off, it runs fine. (until i come to a stop, the engine light and wierd idle). It very rarely actually stalls the engine.
I ran the diagnostic and have no codes (12, 12) ????
Could the MAP sensor possibly be going bad? (without a code) or would this trigger engine light while driving?
Already throughly checked for vacum leaks and egr seems to be fine also, tried it unplugged and made sure it moved, etc.

Anyhelp would be appreciated!

 

Also I have never owned one of these before, but with automatic, 160hp and 220torque it should be pretty quick off the line? It feels slow, very slow.

 

This almost sounds like you have an EGR problem that affects idle and off idle, but not higher rpm operation. Just as an aside, the EGR valve on your engine is vacuum actuated. This could explain why the RPMs fluctuate as they do. I don't believe that the PCM should be opening the EGR valve at idle though... But this could just mean that the EGR vacuum solenoid is not functioning properly.

If, when you ran the diagnostic, the check engine light was not on, then a 12,12 is exactly what I would expect to get out of an OBD1 vehicle. If you can, run the diagnostic when the CEL is on.

 

CEL goes on at idle for like 5 mins then off, I will try shutting car off while CEL is on and checking.
My unplugging vacum to EGR can I eliminate that as a possibility?

 

If the EGR valve is sealing up properly, and you were to plug the vacuum line with a golf tee, bolt, etc, you should notice an improvement if this is the problem. Sometimes carbon can build up and hang the valve slightly open which would have an effect on idle quality.

 

I will pull egr valve out and clean ifneeded. Then I will report back later today!

 

Waited until CEL came on after wierd idle started, turned key off, jumped A,B turned key to on poss. NO CODES just 12, then pause then 12

Pulled egr, everything looks super clean, put back together.
Pulled IACV, it looked nasty with buildup on end, bought a new one $64, installed.
Same problem, it idles fine for awhile then all of a sudden starts idling ****ty and CEL comes on, you drive it, cel goes away. Also noticed surging at cruise.
Coulda badCoolant Temp sensor do any of this?

 

I would first try plugging the vacuum line feeding the EGR valve. If you disconnect the vacuum line at the EGR valve, just stuff a golf tee in the end of the line and drive it around like that.

I'm not sure if an ECT would cause this surging. Typically a faulty ECT would cause the engine to just run rich all of the time and possibly never get into closed loop operation.

 

Going to plug EGR, if that doesnt work, it is for sale $1000.
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