So i decided to pull out the IAC from the TB, since i had all the TPI stuff pulled for injector service. I havent had any real major problems with idling, but wanted to check it out anyways. Man was that IAC point fouled up with carbon! and the spring as well, and the passage ways. Cleaned it all up good with carb cleaner. Cleaned up the TB itself also. So is the carbon fouling normal? I have not had the IAC pulled in the 22 years i have owned the car. Just last year i deleted the EGR, so that should help, yes? Should i expect better idle quality?

 

OK, so now i got a more serious question about this IAC business. What is the screw size for the 7 bolts that hold the IAC cover down to the TB? It is a Torx head, maybe T20, fine thread. I measured it out to be #8-36. About 1" long. I broke one of the screws geting it out, just the head end. I was able to vise-grip the rest of the screw out of the TB. I want to replace them all, since they are all gummed up. I ran a tap in the threads, to clean them up. But went to Lowes to find some screws, and they dont have them. Helper guy checked my screws out, and said they are metric. like #M4-.70. They are very close to the 8-36. So which one is correct? I am gonna try the Chevy dealer, as well as Napa. Need help on this one!

 

Metric M4-.70 sounds right. If you re-tapped the holes to #8-36, then those should fit instead.

I buy my fasteners from Fastenal... Socket cap screw in M4-.70 x 10m length

 

Carbon is normal there. Deleting EGR might help as you said.
And on another note....22 years and same IAC!?!?.....You, my friend, are very lucky! I replaced mine 4 times in the 27 years I owned mine.

 

Well the threads are so close, you could use either! I just want to know what is right. Will check dealer soon. I really need a socket head or torx.

 

Yea, that right, 22 years! And i am sure it is still the original, car had 34k on it when i bought it in '92, now has about 85k. I do take care of it the best i can.
Just need to get the right screws so i can lock the IAC cover down.

 

Well it looks like the metric size M4-0.70 is the winner. Went to Chevy dealer, and he was not much help. But said it was likely metric. Didnt even have screws down that small. But did give me a tip on local hardware store, who might have some. Said dont bother with NAPA. So i found some metric philips head, about the right length. Cap head screws in that size werent quite long enough, darn! they were better screws! But what i got should work, i will work another metric tap down the holes. The hardware store didn't even have size 8-36~! had fine and course for number 10, but not 8. So i am going with metric.