I have acquired a 95' Monte Carlo Z34, but it has a high/fast idle issue. It likes to idle at ~1500 RPM's. I have built the two transistor OBD cable, and have read the codes using TunerPro.

The only code that is thrown is P1650 which is for a malfunction with the #2 quad driver. Alldata indicates that this quad driver is used for the EGR solenoids, and the TCC solenoids.

Another thing that I noted while reading in Alldata is that P1650 will not trip the check engine light, which is on. <- Baffled on that one.

One other thing that I noted while running diagnostics with TunerPro, was that is was stating that the AC Clutch was engaged. So i disconnected the AC Clutch plug on the car, and it still idles at ~1500 RPM's which according to TunerPro the PCM is demanding this RPM levels.

My theory is that since the computer thinks the AC Clutch is engaged then it is commanding the car to a higher RPM. This could be incorrect, but that's kinda what I'm thinking on this now. I will dig on Alldata some more to see if I can find another sensor that would be telling the PCM this information.

If I post a data log of from TunerPro could someone play it back and take a look at it for me?? I'm sure that someone who has experience with interpreting scanner data could spot the problem pretty quickly.

 

i really dont think it is a computer issue causing the high idle. on these engines its more then likely a vacuum leak. i would suggest changing everything from the lower intake gaskets on up. this should solve the issue.

 

that sounds like the top sensor on the throttle body, i had the same issue, but i got a 3.1 and plus obd2 so it could be different than yours, but it sounds like the idle sensor on the throttle body is what it sounds like, prob could clean the throttle body and clean the sensor housing