High reving by itself, weird shifting

Tiny
AWESMINC
  • MEMBER
  • 2000 PONTIAC SUNFIRE
  • 278,000 MILES
My 2000 Pontiac Sunfire, 2.2L 4 door has over the last week or so started to do some weird things.

It usually happens about 20 - 30 mintues into my 45 minute commute (It has happened 3 times of the last 4 trips). At which point the car will downshift and begin to rev very high, regardless of what I do with the pedal.

When I shift into neutral the RPM's will redline with nothing touching the gas pedal.

You can feel the car start to accelerate on it's own, but while in gear it is controlable (usually won't accelerate past 60KM by itself), and if you hit the brakes it will slow down but it feels as if you are two footing it and still pressing on the gas, and as I said if you shift to neutral (or park) it will redline. Shutting the car off and restarting it causes the RPM's to stop redlining but it will still be reving high.

If at a stop and you restart to stop the redline reving, you can shift into drive and reverse and back without it starting to rev uncontrollably again, however the car is idling very high after this happens (normal is usually 600-800 rpm, versus 1500 after this). If you drive even for a few feet however the car begins the redline reving again.

However if you leave the car for a few hours it seems to drive normally again, and I have never had a problem on a trip less than 25 mintues long.

It's an old car, with a lot of K's on it and I don't want to spend a fortune fixing it.

The engine light has been on for the last 2 years after the Fan seized, but since everything is highway driving on this car it has not been replaced.

Any ideas would be very helpful, thanks.

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Monday, February 20th, 2012 AT 12:42 AM

6 Replies

Tiny
RASMATAZ
  • MEMBER
What you need to do here, is have the computer scanned for code/s-go to Autozone free public service -start here
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Monday, February 20th, 2012 AT 12:47 AM
Tiny
BILLYMAC
  • EXPERT
Hi and thanks for the info. This sounds like bad fuel injectors or possible a failing cruise servo. When injectors fail they will spray more fuel into the engine then requested. They will also leak at idle raising the idle.

Cruise servo failure can cause eng to accelerate by itselfeither way both of these issues are very dangerous because it can happen at anytime even while sitting at a stop light or pulling into your driveway.I would have the injectors checked or changed. You can disable the cruise if you want. Good luck Billymac
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Monday, February 20th, 2012 AT 12:57 AM
Tiny
AWESMINC
  • MEMBER
Read the codes from the car today. Only code coming out is the radiator fan, which hasn't worked in two years. Car is always on the highway so the fan was never an issue. Guy at the store thought it might be a throttle position sensor that went or is going bad?
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Tuesday, February 21st, 2012 AT 8:36 AM
Tiny
BILLYMAC
  • EXPERT
Should be a code for that. But anything is possible good luck
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Tuesday, February 21st, 2012 AT 5:04 PM
Tiny
AWESMINC
  • MEMBER
Changed the throttle position sensor and it is still doing it. Disabled the cruise control and also still doing it. If I do get it solved I will post something here, maybe save someone else a headache.
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Wednesday, February 22nd, 2012 AT 3:38 PM
Tiny
BILLYMAC
  • EXPERT
Sorry please repost your question again and one of our gm guys will pick it up and help you further
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Wednesday, February 22nd, 2012 AT 7:19 PM

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