Could it be a bad TPS???

frontshadow

Registered User
OK, here's the symptom. We're moving down the road, with the cruise control engaged when suddenly the transmisson drops from overdrive into 3rd gear. This also randomly happens with the cruise control disengaged and just holding the speed steady.

It does not matter if the car is moving uphill (with a slight load on the engine) or moving on a completely level road (almost no load).
I've tried running the car with the Overdrive disabled and actually have had the car downshift from 3rd into 2nd.

As soon as the downshift occurs, you can remove foot from the accelerator, let the RPM drop and the car will shift back into the gear it was in (prior). Everything works normally. This random downshift might occur 2 times in a mile or perhaps 1 time in 25 miles. I have noticed that I have never experienced it when the car is cold only when warm or hot.

I bought the car new, have never abused it (I'm 51 years old) and it only has 58K actual miles. I just replaced plugs/wires and completely flushed the transmission (new filter also) in an attempt to isolate the problem. No negative nor positive results.

Now, I'm wondering if the throttle positioning sensor might be the culprit. After the car warms up just a bit, I notice a very, very slight "hickup" in the engine while idling. It's very random and almost noticible at all (unless you are familiar with the engine and how it should run). I would not classify this as a engine miss, almost a computer/sensor hickup.

....any ideas???
 
What year SC? To my knowledge this is not a plausibe cause on the early model (89-93) SC's given they have AOD transmissions which are not electronically controlled. Thus the TPS does nada. I would have to check if there is a TPS input to the late model SC's trannies though.
 
Oooops!!..Sorry Duffy, I forgot to say that the SC is a 95 with and AODE transmission.

I appreciate your reply and thanks!! Earnie
 
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