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Air idle control valve

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  • Gold FFM

I was having a high idle at random times. All looked ok on frees an as well. Unless I was looking wrongly.

High fuel consumption - but I put that down to my heavy foot. The iac valve had a wobbly pintel which I think was the issue.

Now it's a lot - and I mean a lot better. Much smoother on idle as well. Fuel economy, whilst not that important, is massively improved 190mile per tank up to 295 per tank!!!!! It never looked like it was running rich either - more air and it chucks more fuel in I suppose

However. I am getting high idle again - very infrequent - and solved by a quick throttle stab - very different fault and believe it's the tps which could do with changing.......... But it's not symptomatic like the iac.

Once the idle went high on mine with the old iac - the only thing that would change it was to turn off and restart.

My throttle jack etc - that's all in the bin - so I can't help with that. Restarting does try to reset the iac though

Only here once

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Thanks. I think my irregular problem may be the ebpv and the throttle Jack stuff. I'll take it off then.

I will though, get one or two iac's from rockauto as suggested. Can never hurt.




Nobody does it better - than Lotus ;)

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  • 1 month later...

After reading this thread I'd thought I'd replace my IAC with the part supplied by Rock Auto.

The car has been running what I would consider pretty good considering I'm currently living with a sheared manifold stud causing a blowing at the manifold. However, possibly because of this issue the car seems to want a restart after first start up or it will stall without higher than normal revs setting off. So for the little money this costs, the possible fuel consumption improvement and its probably one of the easiest installs, I thought I'd get it done.

I would guess that the IAC has never been changed on the car. On removal it was pretty black and there was at least a good few  mm movement in the shaft side to side.

Swapped it over, reset the ECU by disconnecting the battery and then started her up.

As Glyn found, immediate improvement in tick over stability. Much better control / easier throttle control setting off as though the car has an easier time of stopping the revs dropping off when setting off. General low speed running off throttle / little throttle seems much more controlled. Felt as though the car ECU Learning process settled down much more quickly. All quite subtle and probably subjective, but considering I wasn't really trying to fix any specific issue, I'm really pleased I change IAC. I'd definitely recommend it to anyone who hasn't changed theirs in a while or ever!


Thanks to the contributors in this thread who have put in the leg work to track down the correct part no. and info (Barry and Alan). Great work!

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  • 1 year later...

The GM 17112929 (AC Delco 217-427) ISC valve has the wrong pintle shape and diameter.

The GM 17112648 (AC Delco 217-421) ISC valve has the correct pintle shape. The only difference to the OE ISC valve is the wiring connector is offset 45 degrees from the centreline of the mounting holes (the OE valve connector is in line with the holes).

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  • Gold FFM

I have a 427 fitted, and the engine certainly does run well with it, but I also think I have a couple of 421's in stock. It's a 5-minute job (unless your name's Sparky and it's an SE), so I could easily change it to see what the difference might be.

Margate Exotics.

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  • Gold FFM

Yes, Alan I can do it.

I need to check which IACs I have first. I'm fairly sure I ordered some 421s when Derek and I were conversing about it. I will do it when I get a chance, but right now I've got a few other priorities.

Margate Exotics.

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  • 11 months later...

OK, so jury is in...    

Is    217-421  by AC Delco the right part/cone shape?  Same as  AIRTEX/WELLS 2H1018

P.S. They jacked the price of the AC Delco part to $ 80,79 ! (pic 1)


Meanwhile, Delphi CV10151  part (pic 2) costs $27,79, but has a triple sloped cone plunger.  Same as STANDARD MOTOR PRODUCTS AC66 {#17112929, 217427}

Hmm...  I guess, this one is "bad" for idle? Right?


Pic 3 shows Airtex/Welles 2H1020   part with yet another cone shape! More sloped cone

X-reffed to ACDELCO 217411 {#17111826} GM Original Equipment

Is this the right one?


Anyone has a picture of the OE "Lotus" part? Which one REALLY works?

Idle Air Control Valve SE.jpg

CV10151A  DELPHI IAC.jpg

2H1020  Airtex Welles, (Delco 217-411).jpg

Edited by MrDangerUS


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