Fast idle even after replacing my IAC

[alpinecrick]

A bad TPI (throttle position sensor) can cause fast idle too. Although it will usually throw the TPI code.

 

[bigfutz]

A bad TPI (throttle position sensor) can cause fast idle too. Although it will usually throw the TPI code.

I checked the TPS for smooth operation with an ohmmeter, 2.7k-7k sweep if I recall. Couldn’t find a reference to expected values anywhere. I have another GMT400 that needs a TPS I think, but I haven’t measured it yet; I understand a bad TPS can cause a hard shift from 1-2.

 

[evilunclegrimace]

I checked the TPS for smooth operation with an ohmmeter, 2.7k-7k sweep if I recall. Couldn’t find a reference to expected values anywhere. I have another GMT400 that needs a TPS I think, but I haven’t measured it yet; I understand a bad TPS can cause a hard shift from 1-2.

A ohm meter will not show a faulty TPS winding you will need an ocilliscope

 

[bigfutz]

I replaced the TPS, also found the rubber squeegee boot was missing from the connector, which might explain weather/humidity related bad behavior. I also did a IAC reset (without adjusting the throttle plate screw). Seems to be running alot more like it should now, but I haven’t put her through the paces yet.

A little background... I would have random bouts of high idle on crank, hard shifting out of park, and hard shifting in general. Seems like it was ignoring or not reading the TPS, so it was shifting as if I was at WOT: 1-2 > 2000rpm, 2-3 > 3000rpm, etc.

My theory is that the hard shift was due to the torque converter being locked up not slipping as it would with actual heavy throttle. I don’t know s*** about drivetrains; am I even close?