5.7L rough idle when cold

[DrJohnW]

I have a 1999 Chevy Suburban, 1500, 2WD, 5.7L. It has a very rough idle when cold (1000 - 200 RPM but does not stall). The condition improves, and is unnoticiable when at operating tempertature. The throttle position sensor was changed - no improvement. It has new plugs, wires, cap, etc.

[taillight]

Try cleaning the throttle body, IAC(idle air control), and injectors.

[DrJohnW]

Thanks. How do I locate the IAC? I am not familiar with that device.

DrJohnW

[taillight]

It is in the throttle body. Unscrew it and clean it with carb. cleaner.

[GMMerlin]

Originally Posted by DrJohnW

I have a 1999 Chevy Suburban, 1500, 2WD, 5.7L. It has a very rough idle when cold (1000 - 200 RPM but does not stall). The condition improves, and is unnoticiable when at operating tempertature. The throttle position sensor was changed - no improvement. It has new plugs, wires, cap, etc.

Injector poppets are sticking closed causing your concern.
They cannot be cleaned with conventional injection cleaners, only by injecting high pressure nitrogen or by replacing the injection unit with an updated one.

[taillight]

I have had good luck cleaning GM injectors with a Sun Fuel Injector Cleaning Machine. I think I would try that first.

[Kawazar]

DrJohn have you had any luck? I have the same problem but I haven't addressed it yet.

[Captain Ron]

Originally Posted by DrJohnW

I have a 1999 Chevy Suburban, 1500, 2WD, 5.7L. It has a very rough idle when cold (1000 - 200 RPM but does not stall). The condition improves, and is unnoticiable when at operating tempertature. The throttle position sensor was changed - no improvement. It has new plugs, wires, cap, etc.

Check the other post related to this issue. Sounds like an intake manifold crack or bad gasket. Very common, known issue.