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Q: 1997 GM TBI 5.7 : Idle too high

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Hi Peter. I am assuming you also perform repairs. I have a 1997 5.7 GM engine with TBI. I replaced the engine from non-vortec heads to one with vortec heads and an aluminum intake (Edelbrock). The trouble is the idle is too high, cold around 1200 RPM and warm around 1600 RPM. This is in a boat. The problem is many boat mechanics seem to just try different parts until something works. I'm hoping you may have more experience than that. My next step was to remove the IAC to check for deposits. It was fine before I replaced the engine. Any ideas? Is this something you would work on?

Hi there. Check for any vacuum leaks that the engine may have. Look for any vacuum hoses or ports that are not connected. Vacuum leaks on the engine will contribute to the engine having a higher idle. If the vacuum is good and there is no leaks, then check the idle adjustment screw on the throttle body for the throttle stop. You may have to back down the stop as the engine now has a much larger area of induced air into the engine. Reducing the amount of air entering the engine at idle will lower the idle.

If the idle is still high on your engine, then either the IAC or EGR is plugged up.

I recommend removing the IAC and EGR and clean them from carbon deposits.

If you need further assistance with your engine idle, then seek out a professional, such as one from Your Mechanic, to help you.

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