IAC Issues - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

Reply
 
 
 
Thread Tools Search this Thread
Old 07-22-2014, 04:10 PM   #1
Member
Posts like a V-Tak
Thread Starter
 
Join Date: Sep 2008
Posts: 90
Thanks: 0
Thanked 2 Times in 1 Post
Richardyuyu1 is on a distinguished road
Default IAC Issues

Oh it feels good to be back on the forum I haven't had many issues with the car lately until now. I think my IAC is going bad. When I turn the key to the position that turns the fuel pump on(right before starting the engine)shouldn't the IAC retract and let air into the throttle body? I'm asking this because I've had problems with idle at start up, and sometimes during driving when I take my foot off of the gas to apply the brake, the car stalls.
I read online that the IAC should retract when the key is turned to the second position, right before the car is started. Am I right or wrong?
Richardyuyu1 is offline   Reply With Quote
Old 07-22-2014, 08:12 PM   #2
Senior Administrator


Certified Car Nut
 
Mike's Avatar
 
Join Date: Jul 2003
Location: Horseheads, NY
Posts: 15,641
Thanked 995 Times in 772 Posts
Mike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond repute
Default

This is for my 97 Bonneville from AllData....

Quote:
The purpose of the Idle Air Control (IAC) valve is to control engine idle speed, while preventing stalls due to changes in engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle plate. By moving a conical valve, known as a pintle, in (to decrease air flow) or out (to increase air flow), a controlled amount of air can move around the throttle plate. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM.

The IAC pintle moves in small steps called counts. During idle, the proper position of the AC pintle is calculated by the PCM based on battery voltage, coolant temperature, engine load, and engine RPM. If the RPM drops below a specified value, and the throttle plate is closed (TP sensor voltage is between 0.20-0.74), the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle position to prevent stalls.

If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset.

The IAC resets when the key is cycled ON then OFF.

When servicing the IAC, it should only be disconnected or connected with the ignition OFF in order to keep from having to reset the IAC.

The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is open fully, too much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. DTC P0507 may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with possible hard starting and a rich air/fuel ratio. DTC P0506 may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load.
Mike is offline   Reply With Quote
The Following User Says Thank You to Mike For This Useful Post:
WilliamE (07-23-2014)
Old 07-22-2014, 11:11 PM   #3
Member
Posts like a V-Tak
Thread Starter
 
Join Date: Sep 2008
Posts: 90
Thanks: 0
Thanked 2 Times in 1 Post
Richardyuyu1 is on a distinguished road
Default

For years I have had decent to bad idle that would come and go. Then one night the car stalled, but started back up with no problem, this happened about ten times in the last 9 months. Also when the car was in drive and at a complete stop the idle would get really bad and drop to about 700 rpms. And when I would start the engine cold it was really loud on start up for about the first 60 seconds or so. Tonight I installed a new IAC and it'* like I'm driving an new car, all of the idle symptoms are gone and the car is much quieter on start up. And I noticed that my aftermarket stereo is getting more amperage do to the higher rpms at idle. My car is a 98 Bonneville, if you have the original IAC in your car I would change it, you can thank me later.
Richardyuyu1 is offline   Reply With Quote
The Following 2 Users Say Thank You to Richardyuyu1 For This Useful Post:
Mike (07-23-2014), WilliamE (07-23-2014)
Old 07-23-2014, 10:09 AM   #4
Senior Member

True Car Nut
 
WilliamE's Avatar
 
Join Date: Jun 2011
Location: VA
Posts: 3,087
Thanked 418 Times in 376 Posts
WilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond reputeWilliamE has a reputation beyond repute
Default

Glad you found/fixed the problem.
Thanks for updating us.
WilliamE is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
IAC counts 0, no change in performance? Allmachtige Performance, Brainstorming & Tuning 3 11-08-2004 12:29 AM
IAC module macho_mike21 Performance, Brainstorming & Tuning 7 10-03-2004 02:29 AM
IAC Valve Cleaning question.... Hurianek 1987-1991 16 08-19-2004 11:56 AM
IAC Valve ? SSEimatt93 1992-1999 2 03-02-2004 02:13 PM
IAC amy_lynn 1992-1999 2 12-18-2002 11:46 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 11:10 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.