1998 Deville over revving
 

Need help. I own 1998 Cadillac Deville. You folks helped me solve overheat problem...THANKS! Now a problem I have been fighting for over a year. After about 30 minutes, the motor, on it's own over revs. TPS, idle control motor and computer have been replaced. Cadillac dealer service tech plugged in monitor and we drove it. Over rev and no codes. TPS, and idle control motor have been replaced several times. No apparent cracks in intact. Any ideas?

can you provide more detail?


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Over rev
 

in stop and go traffic, or at freeway speeds the car, on it's own, begins to increase in rpm's. Sometimes slowly from 600rpm at idle to 800 to 900rpm. Then it continues to rise, on it's own upwards of 2000rpm and will not back down. Car has to be shut off and restarted several times for the rpm's to come back to normal idle of 600rpm

i understand the stop and go traffic, but it also does that while cruising at freeway speeds, like 65 mph?




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Over rev
 

Yes, also at 65mph. I would have it in cruise control and will start creeping up in rpm. Switch off cruise control and rpm's keep climbing with no input from me....foot off gas....car just keep accelerating

Is car stock? If modded what has been done? Dealer may have Vehicle Data Recorder which can help find problem. Provided car is stock, contact Cadillac Customer Assistance for help. DO NOT expect Cadillac to fix it for free, car is 12 yrs old, GM tech assist can not help dealer with your car because it's too old. The concern is one they should be interested in, especially in the aftermath of Toyota's present mess. Docament who you talked to and what was said. If they seem not to care contact NTSB they will care, no one wants RUN AWAY car on the roadways. As I stated earlier don't expect anything for free, but dealer is the best place to go with this type of concern. If possible don't drive car until cause is determined.

thanks for reply. Will try your suggestions. No mods

I have the same problem on my 1999 Deville, took it to the shop and find out that have head gasket problem too. Is this is related?? I would like to keep my Cadillac. Help!!!!

Is the throttle pedal moving when it does this, or not?:confused:
Were all of the above parts replaced to try to correct this problem, or did the problem occur after replacing something?
Something is telling either the IAC to increase the airflow, or the cruise is coming on.
IF the base idle speed(mechanical setting) is too low, the PCM will command the IAC to open up. This may not happen until the engine is in full "closed loop" operation, but it shouldn't effect anything @ cruise speed.:confused:

Has the throttle body ever been off, and cleaned?

over rev
 

gas pedal does not appear to move, even though my foot is off pedal, and car continues to accelerate. All parts replaced have been to correct the problem. Throttle body came off cleaned and inspected-no cracks and no warping