Perplexed

[captndave737]

My IAC's were at 72 and my TPS at 40. I wanted to get the IAC's down to the 10-20 range. As I slowly screwed in the idle stop screw my IAC's went to 70 and then started going back up! At each little 1/8 turn of the throttle stop screw I would re adjust the TPS to 38-40. It seems no matter what I do I can't get the IAC's below 70! It's in closed loop while I'm doing this.

Any suggestions?

 

[GNRick]

Try cleaning the throttle body and iac with carb or throttle body cleaner. Might be full of carbon.

 

[RUQWKNF]

If it's an original IAC valve, it could be sticking from carbon buildup as GNRick mentioned.
Also, the screw is the minimum air bleed screw, or minimum air adjustment screw. It sounds like the t-body, IAC and IAC housing might need a good cleaning with carb cleaner / brakekleen and a tooth brush, then follow these steps for proper IAC adjustment after you get it back together.

http://www.gnttype.org/techarea/faq/IACresetscan.html

Also, the spring on the IAC could be broken from age / heat cycle fatigue. It's always good to replace a 30+ year old IAC valve with a new one. Once the hard parts are cleaned and or the IAC is replaced, followed by the reset procedure, your numbers will start to behave.

Carbon build ups typically start from oil getting sucked into the system by way of the stock breather tube on the stock turbos inlet bell. This can also be caused from a leaking turbo seal caused from excessive thrust bearing failure on the compressor side of a journal bearing turbo. This lets oil blow into the intercooler and work its way to the t-body & IAC. Signs of this are typically dark discoloration and oily residue on or around the intercooler hoses, around the t-body and vacuum block assembly and oil inside your MAF hose / pipe, or the MAF itself. Which btw, is a quick killer for stock MAF sensors. (oil on the heating element and circuit board)
Hope some of this helps.

-Patrick-

 

[captndave737]

Thanks for the replies. It is a new IAC and I had reset it from the procedure in the Factory shop manual which I have.

It turns out it was just my stupidity. I wasn't turning the engine off between adjustments! After checking the Vortex Buick sight I started with 1 1/2 threads showing, I had been backed off way too far. That got it close and 10 minutes later it was done. IAC's 20 TPS 42.

 

[earlbrown]

You were going the wrong direction too. Backing off on the screw will close the throttle blade and make the IAC open more to compensate.

Restarting the car is very important. As you noticed when you altered the idle 'default' The computer just thought you moved the gas pedal.

 

[captndave737]

No, I was turning it in to open the throttle blade and the IAC count would go up. I wasn’t shutting the car off after each adjustment and it was screwing me up.

I also started with the screw backed off way to much to start with.

Ported pilished heads and intake 212/212 cam, your pistons giving me 9.47:1 compression, precision SLIC and 6262 turbo with a .63 exhaust, 3” external gate down pipe and this is a beast at a measly 17lb of boost compared to the stock setup I was used to for 30 years. Can’t wait to see what it will be like with the Alky hooked up.

 

[earlbrown]

I told you that you'd like the extra bump from the compression and faster burn rate.

If you're running the same exhaust you had before, did you notice more of a 'pop' while cruising or at idle?

 

[captndave737]

Oh yeah, big bump way before boost comes on. I’m running the same 2 1/2” 3 muffler exhaust I was before. I hate noise but it has a nicer sound now. The mufflers are dynomax straight through design. Later this year I’m upping it to the same system but 3”.

 

[captndave737]

No more boat towing either even though blowing away hemi’s while towing is lots of fun.

 

[earlbrown]

That's what I have. ATR single shot with a dynomax race magnum. Ran that since the early 90's (whatever the date is on gnttype.org with my THDP and TE44). When I put my slugs in the sounds and feel was night and day. I dig it.