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Ask Kevin Bourcier Your Own Question
Kevin Bourcier
Kevin Bourcier,
Category: Chevy
Satisfied Customers: 117
Experience:  Owner/Technician at Max Air Mobile
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I have a 1992 K1500 with 96K+ miles. It starts well and

Customer Question

I have a 1992 K1500 with 96K+ miles. It starts well and idles perfect at 1500 RPM in park or neutral. But as soon as I put it in gear (reverse or drive), the RPM drops to 1K or less, the idling gets rough and the engine will stall if I don't start moving the truck. Runs well on the open road, no misses, even when trans drops to a lower gear when climbing a hill.
I hope you can help me resolve this problem as it is a real nuisance.
Dick
Submitted: 1 year ago.
Category: Chevy
Expert:  Kevin Bourcier replied 1 year ago.

hello how are you ?

Customer: replied 1 year ago.
Sorry, I did not know that I had to reply until I received an answer to my question. Awaiting your answer.
Richard Uchic
Expert:  Kevin Bourcier replied 1 year ago.

have you done basic checks ? have you replaced or checked the spark plugs , spark plug wires , etc ?

Customer: replied 1 year ago.
Spark plugs and wires are okay.
Expert:  Kevin Bourcier replied 1 year ago.

okay . 1500 is actually a bit high for the idle on that engine . You may have a vacuum leak at the intake manifold . Get an aerosol can of brake clean and with the engine idling in gear ( rough ) spray brake clean on the intake at the cylinder head and also at the base of the throttle body . Those years were known for TB base gasket and intake manifold gasket leaks causing a vacuum leak which would explain your problem .

Expert:  Kevin Bourcier replied 1 year ago.

thanks

Customer: replied 1 year ago.
What should I expect to see when I spray the brake clean at the two points you mentioned?
Expert:  Kevin Bourcier replied 1 year ago.

the engine idle should change and if the engine is missing or running rough it will smooth out .

Customer: replied 1 year ago.
I sprayed more than one half can of BrakeCleen on the TB gasket and the intake manifold gasket with the truck in gear and rough idling at about 500 RPM. I did not notice any change in the idle speed with either application. Any other suggestion?
Expert:  Kevin Bourcier replied 1 year ago.
Okay that is good . You do not have a gasket leak . Next disconnect the IAC motor on the throttle body , ztart the engine and see how it runs
Customer: replied 1 year ago.
I removed the connector from the idle control valve and started the engine. The rpm jumped to 2500-smooth. I put the transmission into reverse and the rpm dropped to 1250-smooth, no rough idling. The same happened when I put it in drive.
Should I reduce the idle rpm to 1000 and try the same test?