C4 IAC Problems.

[Vettech]

Tried pics but this new ipad when set to smallest widgets has a .HEIR and our Forum wont accept.

But after reading 6E3... I now see its a stepper motor, which is reasonable since it allows the ECM to count the steps and remember what the setting is. All the way closed is "0" - at engine off it closes, engine on it counts out to the remembered idle setting.
It does not go too deep but I would assume it is only adjusting idle when under a 1000rpm.

"A scan tool will read IAC position in steps (counts). "0" steps indicates the ECM is commanding the IAC to be driven all the way in, to the fully seated position, and this is usually caused by a vacuum leak. The higher the amount of counts the more air being allowed to pass the IAC valve. Chart C-2C can be used to diagnose the IAC valve. Also refer to "Rough, Unstable, or Incorrect Idle, Stalling" in Symptoms Section B".

There does not appear to be a test voltage, they only say that coil is more than 20ohms each coil, no opens, shorts, grounds, but always do these checks with  ECM disconnected.

And did notice whilst reading last nite before I spat the dummy trying to upload pics, that the pipe you mentioned has vac from under the middle of the runners via metal tube, then 90° rubber hose into 90° PVC valve into rocker cover. The other side is similar but my pic not so good, I'll have a look on the Blue.

Also if you attempt to read the pulses with digital voltmetre - it will try to average out the pulses and display an equivalent DC voltage reading, whilst not accurate it is indicative that one coil is being driven continuously  - and upon reflection I cant find the magic 4.2Vdc we spoke about  - I think that voltage is to do with the TPS setting.

Ummmm you could actually look at the voltage, since if its a pulse, a CRO would display it, now just where that CRO is, umm the killer chickens amd mice live on that side of the garage......... bugga !!!!!!!

[Vettech]

Sirfixalot.  Just reading on "www@corvetteforum.com" - "iac reset" site in the states.

One chappie was adamant that the IAC should be removed and thoroughly cleaned out, appears lots of dust, carbon & other good stuff builds up causing the pintel tobe either sluggish or jammed up, thus no idle tracking.

Have you gotten any further ?..

[sirfixalot]

Took the throttle body off today & cleaned yes IAC does get heaps of  crap in it.Have cleaned it,  yet to test on the bench I believe the valve part will fly out when power is applied read where you have to put it in a plastic bag with leads attached so you don't loose parts.Tested the 02 sensor this morning with meter appears to be open circuit has anyone tested resistance of sensor? Also found the output wire from computer to one bank of injectors is not captive in plug so will have to make sure it is pushed home when plug installed on computer. Still chipping away will delete heated throttle body when it goes back together. Does anyone know what the spring clips are called that keep cables onto post on throttle butterfly or have one spare ?

[Vettech]

Umm.. progress. I dont think it will spring out suddenly, having said that - plastic bag is a good idea.

BUT ! What ever happens it appears the pintel must not be more than 1 1/8" extended - else when you re-install it, the pintel will crush down onto the seat, with the usual results. Any length less than - ie. 1 1/16" or 1" since when you run thru the reset sequence the computer will drive it in and out to self adjust.

[sirfixalot]

After removal cleaning compressed air lucky if I get 1mm of movement on pintle now soaking with inox spray. O2 sensor now out is open circuit looks like somebody has had a go at it before

[Vettech]

Um - that O2 sensor may have failed way back when you changed address, hense crook running.
How did you go getting it out, my experience with anything exhaust ends up broken, sheared off or siezed bits.

[Vettech]

The IAC plug can be obtained from Jaycars p# PP2114 @ $17.95.
Pack inc both plug & socket, seals & M & F pins.

[Vettech]

Ok - the TB is cleaned, IAC housing modified (no more water), gasket set on its way from Glen at Corvette Corner Vic.

New loom plug fitted, place loop into A & B on ALDL,  Ign on,  IAC pintel drives into port to close air off.
Ign off and it drives out and stops. Ergo the IAC appears to be functioning OK.
I have no idea whether the amount it drves in or out is correct, however, the IAC body is loose in my hand and I can feel it drive out and stop, but upon driving in, once seated, I can still feel it pulsing. I can only assume this is correct.

If anyone has a better understanding please feel free to chine in, once the gaskets arrive, everything will (hopefully) go back together.
The goal on this project is not to have too many parts left over when finished. Tks.