Engine Performance problem
2001 Pontiac Bonneville 6 cyl Front Wheel Drive Automatic 255500 miles
Why would the RPMS in my car start surging up and down while I am driving at normal driving speeds? It usually does this in the afternoon after about 15 or 20 minutes. When I come to a stop sign, I have to come to a complete stop and let the RPMS go completely down. The engine starts racing up and down and I can barely make it home. Please advise.
With that many miles on it there are a lot of possibilities. My first suspicion would be that the throttle body could be worn out and leaking vacuum pretty badly. You could also have an EGR valve stuck open but that should put the check engine light on. That particular engine also has a lot of problems with the plastic intake manifold deteriorating and leaking from the bottom.
A sharp tech could hook up a scan tool and analyze the sensor data and possibly come up with a conclusion.