Idle Air Control question
Thread Starter
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
Idle Air Control question
I may have figured out my no idle issue. I took the IAC off and turned the key on and the IAC just stood there looking at me like I was stupid.
Aren't these things supposed to move some when they get power, or was the IAC correct, I am stupid?
Aren't these things supposed to move some when they get power, or was the IAC correct, I am stupid?
Le Mans Master
Joined: Oct 2008
Posts: 9,758
Likes: 49
From: Houston Texas
Instructor
Joined: Jan 2010
Posts: 174
Likes: 4
From: Austin_Palm Bay_Houston Texas_Florida_Texas
with just the ignition on, the IAC won't budge since the PCM has not yet determined the RPM. The IAC is a stepper motor and will "extend" into the TB to reduce idle, or "retract" to increase idle.....all of which is controlled by signal voltages from the PCM.....
Thread Starter
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
This is the information I have researched. Is it wrong?
An IAC (idle air control) motor is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside the throttle body. The cars computer or ECM (electronic control module) receives information from various sensors and will output signals to adjust the IAC motor in or out to adjust engine idle speed by controlling engine idle air. An IAC motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the IAC control motor to react slowly, either failure can cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak IAC motor. To check the IAC motor remove the unit, with the wires connected turn the key to the "on" position without starting the engine, the IAC should move in or out. If the IAC motor does nothing it has probably failed, replace it with a new unit and recheck system. Note: while the IAC motor is removed clean (use aerosol carburetor cleaner) the passages the IAC uses to control idle air speed, also inspect the IAC for a build-up on the seating (pointed) end and clean as necessary.
An IAC (idle air control) motor is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside the throttle body. The cars computer or ECM (electronic control module) receives information from various sensors and will output signals to adjust the IAC motor in or out to adjust engine idle speed by controlling engine idle air. An IAC motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the IAC control motor to react slowly, either failure can cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak IAC motor. To check the IAC motor remove the unit, with the wires connected turn the key to the "on" position without starting the engine, the IAC should move in or out. If the IAC motor does nothing it has probably failed, replace it with a new unit and recheck system. Note: while the IAC motor is removed clean (use aerosol carburetor cleaner) the passages the IAC uses to control idle air speed, also inspect the IAC for a build-up on the seating (pointed) end and clean as necessary.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Key on, unless the Diagnostic Link is grounded, shouldn't do anything. When you turn it off, the Pintle is retracted to allow in more air for a quick restart. It isn't going to move again until it's started. The IAC test is to warm it up; note idle speed and then turn it off. When you restart - because the Pintle was retracted - it should have an idle that was higher than what you noted, but return to that noted speed within a couple of seconds. If so, the circuit and IAC is working as designed.
If you've been monkeying around with things - particularly since you've removed it; you should reset it: Depress the accelerator slightly and start it; let it run for 10 seconds, and then off for 5 seconds. Restart and it should Idle at +/- 100 rpms from Targeted in Park/Neutral. 50 +/- rpms from Targeted in Drive. Monitor Targeted, Actual, TPS, and CTS with your Scanner.
If you've been monkeying around with things - particularly since you've removed it; you should reset it: Depress the accelerator slightly and start it; let it run for 10 seconds, and then off for 5 seconds. Restart and it should Idle at +/- 100 rpms from Targeted in Park/Neutral. 50 +/- rpms from Targeted in Drive. Monitor Targeted, Actual, TPS, and CTS with your Scanner.
Thread Starter
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
that's the thing, the spindle appears to fully open no matter what I do. If I am understanding you correctly.
When I took it out it appeared to be fully extended, so no air is getting in at all.
When I took it out it appeared to be fully extended, so no air is getting in at all.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
You could reinstall and use the method I outlined to reset it OR carefully retract the Pintle with finger pressure; then reinstall and use the reset procedure. You can also check the coils with your DVM - should be more than 20 ohms across A & B; C & D. Check the ECM circuit with a test light from each harness terminal to ground with the Diagnostic Link grounded, key on, harness disconnected. The light should flash or be steady at each terminal.
Thread Starter
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
You could reinstall and use the method I outlined to reset it OR carefully retract the Pintle with finger pressure; then reinstall and use the reset procedure. You can also check the coils with your DVM - should be more than 20 ohms across A & B; C & D. Check the ECM circuit with a test light from each harness terminal to ground with the Diagnostic Link grounded, key on, harness disconnected. The light should flash or be steady at each terminal.
I still have a fuel pressure drop off problem to contend with but I believe the the no idle and fuel drop off are unrelated. I thought they were related but the more I fiddle with this thing the less I'm inclined to think they are one in the same. reason is, I had the intermittant hard start way before this idle thing reared it's ugly head. The idle thing just makes completing the diagnosis of the pressure thing much more complex because I can't get the thing to idle.
It did try the other day but it was starving for something and it has to be air. Or at least that's the direction I am heading. If you give it just the slightest pedal it runs like a champ. We'll see.
Thanks!! When I do get this resolved I will let everyone know what the issues were and what resolved it.
Oh did I mention I dropped my 10mm socket and extention down in the bay somewhere, probably never to seen again. At least I can't find it.
Oh and as a side note. I did try to reset the thing and that didn't work.
Last edited by RetiredSFC 97; Jan 27, 2010 at 02:45 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Thread Starter
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
Started to throw it across the garage last night. Wanta hear something odd and funny? Obviously I'm not a mechanic, that is for certain. Mechanical but not a mechanic.
I was going through my FSM last night going step by step what the manual told me to do. Couldn't do it, so I said the heck with it and took the whole throttle body off. Still couldn't see what the stupid manual was telling me. So I go get my Chilton manual and it tells me there are two types of these things. One that bolts in and one that screws in. (not to mention the thing wasn't where the FSM told me it was)
The whole time I'm trying to take this thing out I'm scratching my head saying, that sure looks like a screw in to me.
So after all this and breaking two light bulbs in my shop light and losing my 10mm to engine bay heaven, I about threw the thing across the room. Had a beer instead!!!
Update: I don't mind poking fun at myself for doing something stupid so I will. I got home today and looked at my FSM again. Last night in my flustered state I was looking at the J (LT5) instructions and not the L98.
So there you go.
Last edited by RetiredSFC 97; Jan 27, 2010 at 06:53 PM.
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Sounds like an average day in my garage. Agent 86 is right, if you jump the A-B terminals on the diagnostic plug and turn the key on the pintle will go airborn, sometimes never to be seen again. This, of course is only if it is working correctly
Instructor
Joined: Jan 2010
Posts: 174
Likes: 4
From: Austin_Palm Bay_Houston Texas_Florida_Texas
Find that socket man !!! If you don't, it will bother you forever !!!
(-;
Safety Car
Joined: Jul 2008
Posts: 3,966
Likes: 4
From: Made In America
St. Jude Donor '10-'11
Safety Car
Joined: Jul 2008
Posts: 3,966
Likes: 4
From: Made In America
St. Jude Donor '10-'11
Safety Car
Joined: Jul 2008
Posts: 3,966
Likes: 4
From: Made In America
St. Jude Donor '10-'11
Thread Starter
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
I didn't try to shoot it across the garage, this time
http://forums.corvetteforum.com/c4-t...ue-solved.html
