how do i test / diagnose the ls1 iac

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strokedcoupe
MS/Extra Newbie
Posts: 19
Joined: Sun Apr 19, 2009 10:17 am

how do i test / diagnose the ls1 iac

Post by strokedcoupe »

I've installed the 5 jumpers as described. and car runs 1500rpm with idle screw backed out... car was fine on gm. computer.. I've ran the iac test in and out and no change in idle.. I had measured the ohms and wired to the prints that way.. I see nothing on volt meter when test is running.. it is a ms3x diy harness wired to factory connectors..

can attach msq but the stepper is turned on and shows it controlling steps on the dashboard when I bring that gauge up.. just see no difference in idle... would the iac stay at the least state it was in with gm computer if nothing was applied to move it??
this is my 5th megasquirt install but my first ls1 install.. so im not completely ms illiterate.. car runs fine in garage free revving and idling just no idle control..
billr
Super MS/Extra'er
Posts: 6828
Joined: Sun May 15, 2011 11:41 am
Location: Walnut Creek, Calif. USA

Re: how do i test / diagnose the ls1 iac

Post by billr »

"Least state" or last state? Yes, that stepper will tend to stay where it last was if not driven.

When using test mode, set "always on" for IAC current control; then you should be able to read static voltages across the stepper coils. If you aren't seeing those toggle back-and-forth, then post some pictures of the board jumpers. Are you checking for coil resistance and voltages right at the MS DB37 connector?
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