2001 Chevy Lumina idles rough

Tiny
2CARPROS-ARCHIVES
  • MEMBER
  • 2001 CHEVROLET IMPALA
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 76,000 MILES
2001 Chevy Lumina mileage: 76,000. Engine runs great sometimes, other times idles rough and after acceleration engine will not idle back down almost as if the throttle is stuck at about 1800 rpm. As you slow down using the brake and coming to a complete stop, engine continues to run at high rpm until suddenly it will idle back down and begin to idle very rough again at about 700 rpm. Then sometimes, with no particular pattern, the engine will settle down and begin to operate normally again. As long as you continue to drive it after it settles down it runs fine. If you stop and shut off the engine for a few minutes and start it, again the whole process starts over with rough idle and high rpm when driving. I have changed the following parts with no improvement: map sensor, oxygen sensor, spark plugs, pcv valve, idle air control valve, throttle position sensor. I have checked trouble codes and I get an error 33 (map sensor low vacuum, high voltage) and error 44 (oxygen sensor lean exhaust) but these codes appear I think as a result, rather than the cause, of the very rough idle. I have run out of things to try. Can you help? Thanks
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Wednesday, January 12th, 2011 AT 8:22 PM

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Tiny
2CARPROS-ARCHIVES
  • MEMBER
Check for a plugged catalytic converter.
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Wednesday, January 12th, 2011 AT 8:23 PM

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