2001 Pontiac Bonneville RPMS surging up and down at normal

2001 PONTIAC BONNEVILLE
255,500 MILES • 6 CYL • FWD • AUTOMATIC
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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.
Aug 17, 2010 at 5:32 PM
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WRENCHTECH
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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.
Aug 17, 2010 at 5:52 PM