| Re: Anyone ever run without IAC? |
Subject: Re: Anyone ever run without IAC? by CFI-EFI on 2009/4/27 14:54:48 Quote:
The IAC opens and closes as commanded by the ECM in order to attempt to maintain the idle speed. I highly doubt the IAC is causing your lean mixture. Especially not at 68 to 70 mph. Certainly Joe knows computers and programming much better than I do, but one problem I am aware of with cams with a lot of overlap that won't idle, is in the minimum air adjustment. With the idle programmed at a workable speed there is usually still a lope. The spec minimum air adjustment has the throttle blades closed so far that the idle speed is allowed to drop too low. As the engine lopes, and the engine drops below the programmed speed, the ECM/IAC open to raise the speed. The open IAC allows the speed to exceed programmed and the IAC closes. The ECM/IAC can't react fast enough. As the target idle speed is exceeded, the IAC gets closed again. The idle goes from too fast to too slow in a widening range. The idle speed is in a death spiral as the highest speeds and lowest speeds get further and further apart and the engine finally dies. Have your idle speed programmed into your chip where it will maintain a reasonable idle (don't forget the timing advance) and then set the throttle stop screw (minimum air adjustment) 100 - 200 rpm below the idle speed. The higher minimum air adjustment will prevent the idle speed from swinging in such a large spiral. Hopefully that will eliminate the dying at idle. RACE ON!!! |
