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Rough idle, stumbling at cruising speed, no CEL codes


ScoobyDoo82

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Just so this is easier to find in the case somebody else is having this problem down the line, I'll post a topic here.

 

1991 Pontiac Grand Prix, 3.1 V6

 

I've been having a problem with my car lately. When I start it up it immediately runs rough, to the point of nearly stalling. At cruising speeds I feel a slight stumble but otherwise runs much smoother than idle. There are no stored/current codes. Also, once I unplug the EGR valve the car runs perfectly. I eventually diagnosed it to a sticking open EGR valve. However I don't believe it to be the EGR valve itself as I took it off and cleaned it and all the pintles seem to move freely. I also ohm checked all 3 solenoids (digital EGR) and they're all within spec.

 

According to the factory service manual, the EGR is grounded through the ECM using 3 sensors to decide... the throttle position sensor, coolant temp sensor, and MAP sensor.

 

I've already tried putting in a spare ECM, and MAP sensor and the problem persists. I'm kind of at a loss right now because I'm not sure what my next step is as I don't want to disable the EGR and drive it like that. My only other idea is some wiring has rubbed through and is just grounding out all 3 solenoids.

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Just threw on a spare EGR valve for shits and giggles. I got excited because it ran great for a few minutes... then did it again :|

 

Only now it doesnt appear to be stuck open, unplugging it makes no difference.

Edited by ScoobyDoo82
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