Q: 1997 GM TBI 5.7 : Idle too high

asked by on February 13, 2017

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.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Transmission not shifting into reverse.

Hi there. If all of the other gears work and only the reverse gear does not work, then there could be a bent shift fork or the reverse input gear has chewed up the teeth. It is very common for...

seized motor help

You may find trying to overhaul the motor and swapping over all the parts to the new motor may be the best bet to get the vehicle to run without problems. You do not know what you are getting from...

Cadillac Catera Engine overheated. Now the car will not start

If the engine has been severely overheated, there may be serious damage. But don't panic yet. At 250000 miles there could be any number of reasons why your car won't start that may not require major engine work. Your best...

Related articles

A Buyer’s Guide to the 2012 GMC Yukon
When When you want a big SUV that can hold its own, come what may, you’ll be happiest with a GMC Yukon. Although the inside of one of these vehicles can sometimes resemble an upscale hotel room, the 2012 GMC...
How Long Does a Vacuum Pump Last?
Your Your car’s engine is a very complex piece of machinery. In order for it to function properly, there are a number of different components that will have to work together. Among the most important aspects of an engine is...
Symptoms of a Bad or Failing Throttle Position Sensor
Common signs include lacking power when accelerating, rough or slow idle, stalling, inability to shift up, and the Check Engine Light coming on.