High Idle 454 Crusader XL

[km1125]

The IAC should compensate for about ~200 RPM of idle, so when you block it off (fully) then the idle should drop. This causes the ECU to command the IAC open, then when you take your finger off, there is too much air and the idle should pop up, then the ECU commands the IAC back closed until idle is stabilized again.

If your IAC didn't have a filter where the port is (and you know that's where it can suck air), then perhaps you got dirt in there and it's partially blocking the IAC internally.

[bud37]

Source of the post

Source of the post If you blocked the IAC port and nothing happened then the IAC was already closed and the engine is getting air from around the throttle plates or elsewhere ....at idle the generally accepted spec for the IAC is around 40-50 counts..closed is 0 counts, full open is around 150 counts......you will need a scan tool to get on top of that stuff.

I'm not too familiar with how the IAC works. Are you saying that I likely have a vacuum leak?

I just put my thumb over the majority of the hole. Air could still get around it, but it was sucking pretty hard. Blocking the majority of the hole didn't effect the idle RPM at all. Not sure what that means, or what to look for next?...

No I am not saying you have a vac leak, but the possibility exists, more testing is needed.

Now this is my take on this.....Think of the IAC as a trimming device, the spec is to have it open at idle an amount so it can move either way to trim the idle as needed and provide smooth acceleration transition from idle and back from open throttle. So that said there are two ways for air to enter your engine under some control...the IAC port and thru the main throttle bore......so give that some consideration, because if that IAC valve is in fact completely shut and the throttle blades are closed properly and not stuck or plugged, I doubt the engine will run unless it gets air from somewhere, so the best way will be for you to get a tech to connect up to your engine and see what is what. You could throw parts at it and hope......again good luck man, its a process as they say, just got to work thru it and when you are done you will have more wisdom than most......

[mjk1040]

Double check your timing!