1990 gmc 4.3l tbi rough idle

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Tom Clark

Colora, MD

I have a 1990 gmc with a 4.3L TBI engine and it runs with a very rough idle. I have changed or subbed out all emission parts including the ECU and Eprom. Timing was checked and set, plus all cylinders have good compression hot and cold. All vacuum lines are in good shape. Changed O2 sensor 2 times same result. Should I replace the intake manifold gasket as some people have suggested? Any help to track down the possible cause/s will be greatly appreciated.

Magiver

Beamsville, Canada

Tom Clark wrote:

I have a 1990 gmc with a 4.3L TBI engine and it runs with a very rough idle. I have changed or subbed out all emission parts including the ECU and Eprom. Timing was checked and set, plus all cylinders have good compression hot and cold. All vacuum lines are in good shape. Changed O2 sensor 2 times same result. Should I replace the intake manifold gasket as some people have suggested? Any help to track down the possible cause/s will be greatly appreciated.

Make sure your fuel pressure is up, Idle air sensor is working or throttle speed sensor is smooth on a ohm
scale then take it from there if you have not fixed it yet!ps . egr stuck open?

Jonathan

Pickens, MS

Replace the nock sensor an tell me what u thank

rtraider

Lufkin, TX

The common parts that cause this type of problem are the idle air control valve and the TPS.

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