1990 GMC Truck



September, 1, 2009 AT 9:37 PM

Engine Performance problem
1990 GMC Truck V8 Four Wheel Drive Automatic 200000 miles

1990 gmc 350 5.7 it runs rough at low rpms in gear in park or neutral it runs fine and smooth but when I first put it in gear it sputters like it is going to die almost as though it is getting too much gas or to little but I cant say for sure I have changed the oil several times I have also tuned it up with plugs, and wires, and rotor and cap. I have also replaced the fuel filter and air filter. Im extremely frustrated please try to find a way to help thank you


Running Rough


Idles Rough/changed Ects


3 Answers



September, 2, 2009 AT 2:07 AM

Clean out the idle air control valve and see what happens



September, 2, 2009 AT 8:58 AM

Where is the idle air control valve and how do I clean



September, 2, 2009 AT 2:08 PM

The IACV is on the throttle body.

Disconnect the air intake ductwork from the throttle body.

Start the engine, then increase and hold the idle speed to 1,000 to 1,500 rpm.

Spray the throttle cleaner or engine cleaner into the throat of the throttle body, aiming for the idle air bypass port (usually located on the side or top of the throttle body opening). Give this area a good dose of cleaner (about 10 second's worth).

Turn the engine off to allow the cleaner to soak into the IAC passageway.

Wait about three minutes.

Restart the engine, rev and hold at 1,000 to 1,500 rpm, and repeat the cleaning process again.

Turn the engine off again, and reattach the air intake ductwork to the throttle body.

Start the engine and rev and hold to 1,500 to 2,000 rpm until no white smoke is coming out of the exhaust pipe.

If this fails to make any difference, you can remove the IAC valve from the throttle body and spray cleaner directly on the tip of the valve and/or into the ports in the throttle body. Let the cleaner soak awhile, repeat as needed, then reinstall the IAC valve, start the engine and run it at 1,500 to 2,000 rpm as before until no white smoke is seen in the exahust.

If the idle speed still surges after this, the IAC valve is defective and needs to be replaced

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