Intermittent High Idle and Occasional Hesitation on Acceleration

[mtbadbob]

I did change the coolant temp sensor last year sometime thinking that could be the issue (that was before I got the ALDL cable so I had no real data to go on at the time) - I doubt my old one was defective since nothing changed and the ECU is getting proper CTS readings.

There certainly is some sort of input to the ECU on gear selection, at least on my 1989. It doesn't seem to know which gear you are in, but I can watch the ALDL data and it correctly changes the flag from PARK/NEUTRAL to DRIVE as I shift. I have a TH400 so no overdrive.

Yeah, I was thinking maybe GM added that gear selector sensor with the GMT400's, as my '89 has a granny 4 speed, so I don't know! I know prior to '88, there is northing to that effect.