Intake Manifold Runner Control (IMRC)

[32sho]

I have a code 551 with no other faults. The butterflies appear to close on start up. The car runs a little rough at idle but that may be normal with 255K on the car. I checked the solenoid and it is reading 75 ohms which is within range and it has 12 volts going to it. When i put a vacuum on the runners they open. When I start the car they close. When I replaced the PCM (eec) with a used one the fault remains. What gives with this code and what else can I check? Should I replace the IMRC even if it Ohms out as good?

 

[projectSHO89]

I've run into a few PCMS that had bad monitoring ports for the IMRC solenoid operation.

Usually, the owner elected to just ignore the fault code since the system otherwise worked correctly.