how to reset the IAC

[King_berald]

gday i was reading that to reset the IAC, you need to rev the car to 3000rpm for 8 seconds, which would be easy enough if my damn holden had a tacho.....how do i do this without a tacho?

[Cheap6]

Don't bother; just drive the car. The position of the IAC is relearned by the ECM after each shutdown and restart and will learn "first guess" idle positions in the interim. If you have had the IAC valve out for some reason you may find that it is initially "wrong" but it will soon be adjusted automatically.

Cleaning it and the throttle (with a cloth + kerosene not carb. cleaner) may help if the car has an intermittent idle speed problem.

[Brett_jjj]

gday i was reading that to reset the IAC, you need to rev the car to 3000rpm for 8 seconds, which would be easy enough if my damn holden had a tacho.....how do i do this without a tacho?

The VN,VP and VR V6 workshop manuals all say to rev the engine at 3000 rpm for 8 seconds to reset the IAC,so its definitely necessary on the VN, VP, VR,V6 engines.Im not sure about the V8 engines in these models.The VS V6 workshop manual doesnt mention this proceedure at all anywhere,so it must have changed for the ecotec version of the V6, and is no longer necessary.Maybe its because the ecotec is MAF based,the earlier ones were MAP based.
Anyway,to rev the engine to 3000 rpm without a tacho,just open it up to about a quarter throttle or thereabouts for the 8 seconds,it might be a bit less than a quarter,it might be a bit more, so just estimate when its reving rairly well but not heaps fast.Just as long as its held at around a quarter throttle,it should be about right.

[Cheap6]

The VN,VP and VR V6 workshop manuals all say to rev the engine at 3000 rpm for 8 seconds to reset the IAC,so its definitely necessary on the VN, VP, VR,V6 engines.

My point is why do that when simply driving the car will achieve the same thing?

[Brett_jjj]

My point is why do that when simply driving the car will achieve the same thing?

Maybe the IAC doesnt reset properly when driving it along,otherwise you would think that they would just say to drive the car as normal to reset it.In saying that,Ive removed/disconnected stuff from these engines heaps of times before, and Ive then forgot about doing the idle reset proceedure,and its been ok still.

[Cheap6]

It resets properly, provided the engine stays above 3000rpm long enough, whether driving or revving freely. It also resets at each engine switch off and restart. At switch off (as with a forced reset) the IAC is driven closed the full 256 steps i.e. sufficient to close the valve regardless of its initial position (unless it sticks) then is opened several steps in preparation for the restart.

Without a reset, the IAC will learn the steps required for maintaining idle speed by trial and error. The IAC steps assumed in the ECM (and shown on Tech 1) may or may not accurately reflect the position of the IAC but will work OK until a position reset occurs.