Chevrolet Repair: Check engine light code 77, upper intake manifold, high mileage

Question
Hi Mark,

I have a 1995 Lumina with a 3100 engine with high mileage (270K+ miles). The Check Engine light keeps coming on with Code 77 (Solenoid #3) every few months. The plenum keeps clogging with carbon build-up, which I clean out every time. I've also had the EGR valve checked, and it is OK.

Do you have any idea why this plenum would keep getting plugged with carbon? Is there another sensor/part that I need to check to get the exhaust "cleaner" (less carbon)?

Thanks for your help,
Daryl Temple

Answer
Hi Daryl, I have seen this before but have always had good luck just cleaning the passage for the EGR valve and this corrects the problem. If it is solenoid #3 maybe you should just replace the valve to be sure that it isn't the problem. Also be sure the passage is clear from the valve through the intake. They plug right at the point where the port enters the upper intake manifold.

Sorry I'm not much help

Mark