My chk eng. lite yields codes P-1537 & 38 "Intake Manifold Runner Control Stuck Open". If IAC is stuck open would engine still run good at idle? Cleaned MAF, IAC, new air filter. Truck runs perfect at idle with only an occasional buck or misfire upon acceleration at highway speed. Checked for vacuum leak off
PCV to elbow, not an issue. Any ideas appreciated!!!

 

Hi mgb150 and welcome to FTE

The IMRC and IAC are different. The IAC just controls the idle speed. The IMRC works sorta like a 4 barrel carb. Your intake manifold has 2 ports for each cylinder. It opens the second set of intake ports when under a heavy load or high rpm.

Possible causes: (generic list)

Leaky vacuum reservoir.
Damaged vacuum lines.
Damaged vacuum solenoid.
Damaged vacuum actuator.
IMRC actuator cable/gears seized.
Cables improperly routed (binding) or seized.
Damaged/disconnected IMRC housing return springs.
Lever/shaft return stop obstructed/bent.
Lever/shaft wide open stop obstructed/bent.
IMRC lever/shaft stick/bind or disconnected.
Open IMRC control circuit.
Open VPWR circuit.
Shorted IMRC circuit.
Damaged PCM.

 

Thanks Racerguy, it was a vacuum leak! The lines going to the reservoir. I wish they were all a 15 cent fix.

 

Thanks for letting us know what fixed it