Will the Throttle Position Sensor create large and rapid swing in engine RPM?


Asked by Feb 14, 2013 at 04:41 PM about the 1988 Chevrolet Beretta

Question type: Maintenance & Repair

Howdy, my engine starts cold and races up to 1500 RPM.  After it warms up it again increases RPM to 3000.  I have read the engine light by ALDL flashes, however, the continual 1 long and 2 short continues flashing while the rad fan is on.  I have found the TPS is not attached to the TBI properly.  This vehicle did receive a new ECM in 2008.  I have not been successful in getting any flashing codes other than the usual reciprocating 12 with the fan on.  Any ideas.  Could a poorly mounted TPS cause the radical RPM behavior?  Other than the above this is avery good low mileage vehicle that has been well maintained by the purchasing owner.

1 Answer


Yes it could. Most tps are fed with 5 volts. The output signal wire should read about .5 volts at an idle and 4.5 to 5 volts at full throttle. As you move the throttle you should see a gradual increase in output voltage. It should be a smooth increase and decrease as throttle is moved. If it is not smooth or not registering the above voltages at idle or full throttle it needs to be replaced. Hope this helps.

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