How Do You Reset the IDLE?
LS/MFT
Joined: Jun 2000
Posts: 5,874
Likes: 0
From: Cary IL
St. Jude Donor '09-'10-'11-'12
Assume you used a new IAC and that you do not have a FSM.
First, did you pre-set the pintle?
"Measure distance between tip of IAC valve pintle and mounting surface. If greater than 28 mm use finger pressure to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage."
[Install step three -- from page 6E3-C2-17 of FSM]
Reset IAC pintle valve position:
a. Depresee accelerator slightly.
b. Start and run engine for five seconds.
c. Turn engine "OFF" for ten seconds.
d. Restart engine and check for proper idle operation.
First, did you pre-set the pintle?
"Measure distance between tip of IAC valve pintle and mounting surface. If greater than 28 mm use finger pressure to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage."
[Install step three -- from page 6E3-C2-17 of FSM]
Reset IAC pintle valve position:
a. Depresee accelerator slightly.
b. Start and run engine for five seconds.
c. Turn engine "OFF" for ten seconds.
d. Restart engine and check for proper idle operation.
Safety Car
Joined: Dec 2006
Posts: 4,290
Likes: 6
From: St Marys GA
On an L98, the base idle speed is also set via a setscrew on the TB, IIRC. Close the IAC (I forget the procedure to do this, it's somewhere on here), then unplug it so it stays closed. Then adjust the idle setscrew so the idle is around 450rpm. Then you're good to go. The screw is on the top, driver's-side of the TB, and I think comes covered with a plastic cap over the screwhead from the factory. I forget if it's hex or Torx.
Corvette Enthusiast
Joined: Oct 2007
Posts: 6,790
Likes: 2,696
From: So. Cal.
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On an L98, the base idle speed is also set via a setscrew on the TB, IIRC. Close the IAC (I forget the procedure to do this, it's somewhere on here), then unplug it so it stays closed. Then adjust the idle setscrew so the idle is around 450rpm. Then you're good to go. The screw is on the top, driver's-side of the TB, and I think comes covered with a plastic cap over the screwhead from the factory. I forget if it's hex or Torx.
Safety Car
Joined: Dec 2006
Posts: 4,290
Likes: 6
From: St Marys GA
Off of Vader's page:
Setting TPS and IAC on an L98:
http://temp.corvetteforum.net/c4/vader86/tpsiac.html
Setting the base idle on an L98:
http://temp.corvetteforum.net/c4/vader86/baseidle.html
Setting TPS and IAC on an L98:
http://temp.corvetteforum.net/c4/vader86/tpsiac.html
Setting the base idle on an L98:
http://temp.corvetteforum.net/c4/vader86/baseidle.html
Team Owner
Joined: Jul 2004
Posts: 28,357
Likes: 3,253
From: Hartford WI
I don't think there is too much to set in the idle since it goes off what the ECM tells it to do. IOW, it will try to open the IAC and if that doesn't work, it will change pulse width and spark advance. That said, the best method I have found is this:
1. Make sure your timing is right
2. Get the car to operating temp
3. Adjust the base idle screw in or out till you see that you have 15-20 IAC counts on the scanner.
4. Set the TPS at 0.54V
1. Make sure your timing is right
2. Get the car to operating temp
3. Adjust the base idle screw in or out till you see that you have 15-20 IAC counts on the scanner.
4. Set the TPS at 0.54V
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Every GM Service Manual I've seen has spelled out the procedure I've outlined. Leave the Minimum Air Screw alone - there's no reason for it to need adjustment. If it isn't right, air flow is restricted (fix the restriction ie, clean the throttle body, replace the air filter) or the throttle body is getting air from somewhere else. Most IAC's aren't broken either and will do the job with everything cleaned up.
Burning Brakes
Joined: Sep 2004
Posts: 1,011
Likes: 0
From: Texarkana TX
Every GM Service Manual I've seen has spelled out the procedure I've outlined. Leave the Minimum Air Screw alone - there's no reason for it to need adjustment. If it isn't right, air flow is restricted (fix the restriction ie, clean the throttle body, replace the air filter) or the throttle body is getting air from somewhere else. Most IAC's aren't broken either and will do the job with everything cleaned up.
Thanks. That summed it all up for me. The thing is...I cleaned mine and now when I first start my vette it idles at 1500 RPM! That is too high for me, as my gas mileage has fallen. So. ???????
Instructor
Joined: Jan 2007
Posts: 112
Likes: 0
From: Belleville Wisconsin
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
As posted - I've never seen a GM Service Manual that didn't outline this procedure - LT 1 guys seldom monkey with the screw (seems to be an L98 thing), so hopefully you just cleaned things up. Otherwise, Base Idle for everything up to Electronic Throttle Controls is 450 rpms, inluding 4's & 6's, port, tbi & sequential injection.
