GMC Troubleshooting Questions? Ask a Mechanic for Answers
Welcome, I'm Chris (aka Moose) I prefer to work when others don't, I am here around lunch and after dinner till after midnight.
At operating temp in park, what is the idle speed now?
Any warning lights on?
it is 8 to 9 hundred. The car does 10 mph in drive when hot with my foot off the gas pedal transmission in drive
Thanks for the extra info.
The tach has small graduations . I estimate 825 to 850 transmission in park motor warmed in operating temperature.Car will go 10 mph in drive with foot off the gas. Very hard on driveline when shifting into drive.
The idle speed spec is 750-900 so your right in the middle and the idle speed is electronically controlled by the computer and the idle air control valve. You can try a new IAC valve but I highly doubt it is going to bring the idle speed down any more. You may also want to clean the throttle body, it could be gunked up and possibly stuck barely open.
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Using the a/c lowers it . Eliminates drive line bang when it is shifted into park. I need to keep another approach. Can I trick the computer to believe the ac is running
The AC lowers the rpm because the compressor clutch is engaged and dragging the engine down. The engine would need a load on it to pull the rpms down, there is not a way to trick it. If you did trick the PCM with out the AC actually on, the rpms would be higher. Are you sure you do not have a pressure issue with your transaxle pressure causing it to harsh engage?
The transmission was rebuild back in 2014 using my old transmission and I checked out the garage and met the tranny mechanic before I employed him It could be what your saying . If it is how can it be modified? How to test ??
You would need to perform a pressure test on the transaxle as your first step.
If its high then there is a concern with the valve body or pressure control solenoid.
Hello again Chris here,