Mooney78865

I have a 91 C4 automatic, stock exhaust with 104,000 miles on it and I continue to get a 32 EGR system trouble code. The check engine light comes on at freeway speed under constant throttle conditions. Once you turn the car off, and re start, it is gone until you are at speed and under constant throttle.
No other codes come up in history except 32.
I have replaced the EGR valve, cleaned the EGR port (runner) in the plenum, replaced the solenoid and checked everything else I could think of, or read about.
The car runs like a top, just the annoying check engine light. And in my Communist state (read California) that is the death nail for passing smog...
Any thoughts would be appreciated.
Smogs not due for another few months by the way......

65Z01

Indeed your symptom means that the ECM is calling for EGR and does not "see" it.

Have you checked the vac solenoid that energizes the EGR valve?

Your '90 does not have the earlier EGR Temp switch. Instead I believe it uses the MAT reading. You might check that the MAT sensor under the plenum is functioning properly. If you have a scan tool the check will be easy.

Cliff Harris

Check all the vacuum lines associated with the EGR valve. In my case the one between the EGR solenoid and the EGR valve had melted and there was a hole in it.

I think the ECM looks at the O2 sensor for a change in AFR to determine if the EGR valve opened.

Mooney78865

Vacuum lines all check out and I have replaced the EGR solenoid. Should I not see a code for the MAT or O2 sensor along with the EGR code if they were faulty? I did clean my MAT sensor while I had the plenum off to replace the EGR.