Hey guys new here but im sick of beating my head against a wall. :banghead: I have a 2001 Alero with a 3400. You start the vehicle and the idle starts to climb and then willl hang out at 2,000+ rpms. I have replaced the IAC, TPS (twice) and harness, cleaned the throttle bore and the problem still persists. If im sitting at a light in gear you have to stand on the brake pedal to keep the car from taking off. When this starts it also shifts late too. If it does start to do it and I unplug the TPS its ok for a little while but comes back. Any suggestions?

Welcome to AF.

Have you checked for a possible vacuum leak at the intake manifold area. A loose or bad vacuum line will cause a high idle. Also, I would check the input voltages (PCM reference) to the IAC and TPS and for a correct output from each sensor.

Welcome to AF.

Have you checked for a possible vacuum leak at the intake manifold area. A loose or bad vacuum line will cause a high idle. Also, I would check the input voltages (PCM reference) to the IAC and TPS and for a correct output from each sensor.

Thank you. I checked for the leaks with a vacuum gauge and it pulled a solid 19"/hg at idle. This problem started and so I did the lower intake gaskets cause they were leaking as they all do and the problem not only persisted but has gradually gotten worse. I have not checked voltage at either sensor though. I will do that thoguh. In the meantime any one else have any ideas?

Man this place is great...39 views and one stinkin reply. Thanks for nothing.

Did you ever check the voltages at the TPS with a DMM? At the input there is a 5 volt reference signal from the PCM module. On the output of the TPS will be a DC voltage ranging from 4.0 at idle to about 4.5 volts WOT depending on where the throttle position is. The PCM uses TPS feedback to help establish a proper idle. If the sensor outputs are good then that leaves a possibility of open/shorted wiring between the sensors to the PCM or a problem with the PCM module itself.

Since the LIM gaskets were replaced make sure all vacuum lines are in the right locations, especially at the MAP sensor located behind the upper intake manifold.

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