Questions and Answers

Starts With A Roar Q. Dear Vincent, The problem I have recently is when I start the vehicle, the engine roars for a few seconds, then settles down to normal idle speed. It seems like an excess amount of fuel is being delivered to the engine for a brief moment. I would appreciate if you could provide me with some clues on where to start the diagnosis.

1993 GMC Suburban
5.7 L Gas V-8
Auto Transmission
98,000 miles
Throttle Body Fuel Injection
ABS Brakes P/S, A/C, Cruise

Thank you,
Armen

A. You have an Idle Air Control (IAC) valve on that throttle body that meters air through it to control idle speed. It may be bad or gummed up with carbon. Also could be a vacuum leak that is letting air into engine that is not being accounted for by the IAC valve. Most likely place for this to happen is the throttle body base plate gasket. They get "sucked" into the manifold. You could confirm this by lightly spraying carburetor cleaner around the base of TBI and see if idle speed is affected. A bad TBI gasket will usually make it idle high all the time though.

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