2004 Chevrolet Trailblazer
Repairs- new alternator
Question = i have a 2004 trailblazer when i turn on the a/c the vehicle idles
down even when in driving it so i turn the heater on and it did the same.
Answer: The problem you are experiencing is the engine is not getting
enough air when the extra load of the air conditioning is put on the
engine. This is solved by a simple procedure. You need to clean the
throttle body assembly and that will take care of your problem.
Remove the ducting and plastic air intake that attatches to the throttle
body so you can access the throttle bore and blade. Use a good
cleaner, brake clean is recommended, and clean thoroughly with a
rag. Get inside the bore good and clean the throttle blade too. You
really need to make sure you get all the carbon build up cleaned off
or you will still have the same issue. Once finished, reinstall the
ductwork between the throttle body and air cleaner and go drive the
Trailblazer. It might take a few minutes to get the rest of the cleaner
burned out of the system, but after a short drive, the engine will have
learned a new idle setting and you won't have it idle down or stall out
when you turn on the air conditioning.

Chevy Trailblazer Very Low Idle