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How does the IAC really work !! 700 1985

posted by  dan52 on  Thu Sep 23 10:55 CST 2004
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Thanks for the informative reply. You have added to my understanding which is always a good thing.

I haven't found the time/energy to trace out the wires from the ecu connector. Maybe it is time. Better yet, time to invest in the electrical manual for this car. I guess I'll have to get the scope out and look at the IAC signals after tracing the harness.


When I adjusted the throttle body, I followed the FAQ procedure to a T. I did loosen the switch to make sure it was not acting as a false stop for the butterfly valve. I set the stop screw only 1/4 turn beyond 'touch'. Then I adjusted the switch to click with 0.15 mm shim and to not click with 0.45 mm shim. There was a pretty thick ridge of varnish in the throttle body before cleaning. I used throttle body intake cleaner only, no tools or undue pressure to remove it. I suspect the thin 'halo' is the result of abrasion of the brass plate on the ridge of varnish. (???)

The base idle screw is not fully in, but as I said, if I adjust it with the engine running, the idle does not move noticably. I just figure that as I adjust the screw, the ecu conteracts by moving the IAC in the opposite direction. I'll try it by clamping the air hose and see if I can get a 'correct' result. I am convinced that the procedure of closing the IAC for setting the base idle is to make sure that the "home" position of the IAC is set to provide the most latitude for the ecu to keep the idle at 750+/-. I would assume that this is near the 1/2 way point of the IAC range, but that is not for certain.

Again, thanks for your response. If I learn something new, I'll post it here for all to share.

Dan





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