Who is buying the next beer. My neighbor thinks his LT1 is idling too fast and thinks there is a way to mechanically (turn a screw etc.) to lower the idle. I keep telling him the idle is set within the ECM and cannot be lowered except by re-flashing the prom.

Who is correct?

 

You are both right to some degree. Yes the idle is controlled by the ECM by using the IAC at idle to control the commanded idle rpm. But, if the set screw on the throttle blade is set too far open then the IAC will likely be at its closed position to try and bring down the idle, but will not be able to as the throttle blades could be set too far open.
You need to find out where the IAC is at idle and from there perhaps the throttle set screw can be played with.
What rpm is he idling at?

 

Thanks for the reply Frankie. He is idling somewhere around 800/900 RPM. However when sitting at a stop as soon as he releases the brakes the car really begins to move forward without touching the gas and he would like to get it down to about 600 RPM. Is this normal with other LT1's with auto trans?

On the left side of the throttle body where the throttle cable is attached there is a small (what we assume is a) throttle stop screw sticking out. On my LT4 you cannot get to the head of the screw because the opening is blocked off with a small extension on a plate.

However on his LT1 the plate extension is not in the design and you can see the hole opening that "almost" exposes the screw head but there is not enough clearence look inside the hole to verify the screw head type or to get an allen head wrench or small screw driver in to make an adjustment. If we could see the head type we could bend a tool to get in to adjust it easily.

Because we could not adjust the screw, last night we were successful is prying back the stop on the throttle linkage just enough so at a cold idle the linkage was not touching the the idle set screw. The RPM did not change. Today he is going to drive it to get water and oil temps up to see if there is any change when hot that allows the throttle plates to close a little more allowing the bent linkage to again touch the set screw....but I don't think it will work.

That set screw is there for a reason but I don't know what it is. If we leave the linkage bent, not touching the set screw in all operating conditions, will there be possible damage to the throttle plates or IAC sensor?

Thanks again.

 

Be careful of bending anything mechanically that the ECM doesn't know about, ie. that could throw the throttle position sensor off of what it thinks it's measuring... could screw with the fuel tables and all... other than that this is out of my know-how...