89 Cavalier runs rough when warm

Tiny
EUGERSPEED
  • MEMBER
  • 1989 CHEVROLET CAVALIER
Chevy cavalier, 1989, 158,000km's, auto, 2.0L ; I recently did a desperately needed tune up : spark plugs, air & fuel filters, pcv valve, throttle body clean, lucas fuel system treatment, coolant & thermostat, tranny fluid & filter and it ran great for around 300km's then started a problem.

When cold the car runs great and as the car reaches a certain operating temp it develops the following symptoms. The idle starts hunting roughly with the rpm's low enough to barely keep it running in park or drive. When you pull up to a stoplight the car will sometimes stall, but it always starts up again. Then when you hit the gas it'll stumble/hesitate throughout the rpm range UNLESS you have WOT then it pulls strong accompanied by blue smoke. I also noticed a smell of gas in the exhaust telling me that it runs rich.

When checking the codes I get 33 and 45, so before I start throwing sensors at the thing, what can I do to pinpoint exactly what is needed.
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Monday, June 18th, 2007 AT 5:43 PM

7 Replies

Tiny
JACK42
  • MEMBER
Code 33 is manifold temp too low, might be the Intake Air Temp sensor. Code 45 is an EST (electronic spark timing) problem. Try unhooking the neg cable for a few minutes, then drive it and see what codes come back
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Monday, June 18th, 2007 AT 5:57 PM
Tiny
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I unhooked the battery to clear the codes and see if it would make a difference with no avail. The car runs the same and the same codes come up. What else can I do?
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Monday, June 18th, 2007 AT 6:00 PM
Tiny
JACK42
  • MEMBER
Try a new IAT (intake air temp) sensor, see if that gets rid of the code 33. We'll go from there
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Tuesday, June 19th, 2007 AT 7:43 AM
Tiny
EUGERSPEED
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According to everything that I have seen on-line and in manuals regarding this vehicle
-code 33 is MAP sensor signal voltage was too high (low vacuum) for at least 5 seconds when throttle opening was under 2% and
-code 45 is Oxygen sensor voltage was above specification (rich exhaust indicated).

Would a faulty IAT effect things to throw these two codes out?
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Tuesday, June 19th, 2007 AT 5:25 PM
Tiny
JACK42
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My bad, looked it up for a different engine vin #. Try a MAP sensor first, if it is off it will think that the engine is getting a different amount of throttle than it is actually getting. Honestly an o2 sensor wouldnt hurt at that mileage either, they have reactive material in them that fades over time
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Wednesday, June 20th, 2007 AT 8:00 AM
Tiny
EUGERSPEED
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UPDATE: MAP sensor was replaced and solved the problem. Car runs beatifully now!
THANK YOU!
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+1
Thursday, June 21st, 2007 AT 8:33 PM
Tiny
JACK42
  • MEMBER
Glad to hear it
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Friday, June 22nd, 2007 AT 7:51 AM

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