2002 Elantra Cel

Wife has a 2002 Elantra with automatic transmission that was purchased new and has been trouble free since today. She stated that the check engine
light went on and the rpms on the tach increased significantly but the vehicle would only allow a maximum speed of 20 mph. She then pulled over as the engine was revving too high and shut the ignition off and called me. I was able to drive the car home without incident and none of the symptoms the wife had encountered. The check engine light was still on though.
I scanned for trouble codes and came up with one: engine PO121 Throttle Position Sensor implausible signal. No codes for the transmission.
I cleared the code and it did not return after starting and shutting the engine off several times. What did happen as I placed the transmission into drive or reverse was the speedometer jumping from 0 - 140 while barely moving in the driveway. It would stay at 140mph and not return to zero until I either placed the vehicle into drive or reverse again. The needle just keeps swinging back and forth erratically.
Any assistance would be appreciated.
Thanks
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paul hodson wrote:

Sounds like it may be a flakey speed sensor.
Matt
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On Sun, 15 Oct 2006 23:45:04 GMT, "paul hodson"

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Start with replacing the throttle position sensor. The code and symptoms are consistent with dirty contacts inside the sensor. This is a common problem with '01s and '02s.
The speedometer problem is probably a different issue. If it happened only while the diagnostic tool was connected, it's possible the tool was interfering with the speed sensor signal. Otherwise, it's probably an issue with the cluster itself.
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Thanks for the assistance. I replaced the TPS and all appears to be fine now. The scan tool was connected when the speedometer was acting crazy. This has not repeated itself.
Thanks again.

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