Min Idle Speed & TPS Question
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by redsand
I am wondering perhaps then if I may have a bad IAC.
When I disconnect the IAC, the idle speed IS set at 450 currently. Plugging the IAC in, it does not seem to be "seeing" that setting. Any other ways that you've checked if your IAC is faulty?
When I disconnect the IAC, the idle speed IS set at 450 currently. Plugging the IAC in, it does not seem to be "seeing" that setting. Any other ways that you've checked if your IAC is faulty?
Originally Posted by CFI-EFI
That proves the IAC motor is working. It closes to set the minimum air, but it opens too far for a proper idle. It is moving.
RACE ON!!!
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Try this when the engine is idling at 1000 rpms and won't idle down, put the trans in Park (assuming you have an auto trans), or neutral and set the parking brake (for manual).
Raise the hood and visually check to see if the TB lever is firmly against the little torx head screw you used to adjust the minimum airflow setting (when you set the 450 rpm setting earlier). If there is a gap, even the smallest gap, between the TB lever and the screw, your butterflies are being held open.
Next, use your hand to see if you can manually push the TB lever FORWARD to the closed position.
If you can and the idle returns to the rpm you're looking for, that tells you that the TB butterflies are sticking in a very slight open position, resulting in the high idle. Try using some grease on the TB shaft to free up its movement.
Also,
If you CAN'T push it more, check that the 'C' clamp that holds the flexible accordian to the TB (fits between the MAF and the TB). Sometimes, that clamp can interfere with the complete closing of the butterflies.
The only way I know of the check for the proper operation of the IAC is to use a data logger, like Diacom or a ScanTool to see what the IAC counts are and to see if the counts change up and down as the IAC pintel moves inward and outward controlling the idle speed.
As I written before you MUST make sure that all the vacuum hoses are properly connected and none of them is leaking due to, perhaps, cracks in a dried out vacuum hose. That's basic stuff that has to be verified before going off the deep end and over-diagnosing this problem.
Always verifiy the basic things first. I wish I had a dollar for everytime someone has posted about a problem, we'd all spend days suggesting things to check (some even recommend changing certain parts) ONLY to find that the guy had failed to check a very BASIC thing which turned out to be the cause.
The Devil's in the Details.
Keep us posted.
Jake
Raise the hood and visually check to see if the TB lever is firmly against the little torx head screw you used to adjust the minimum airflow setting (when you set the 450 rpm setting earlier). If there is a gap, even the smallest gap, between the TB lever and the screw, your butterflies are being held open.
Next, use your hand to see if you can manually push the TB lever FORWARD to the closed position.
If you can and the idle returns to the rpm you're looking for, that tells you that the TB butterflies are sticking in a very slight open position, resulting in the high idle. Try using some grease on the TB shaft to free up its movement.
Also,
If you CAN'T push it more, check that the 'C' clamp that holds the flexible accordian to the TB (fits between the MAF and the TB). Sometimes, that clamp can interfere with the complete closing of the butterflies.
The only way I know of the check for the proper operation of the IAC is to use a data logger, like Diacom or a ScanTool to see what the IAC counts are and to see if the counts change up and down as the IAC pintel moves inward and outward controlling the idle speed.
As I written before you MUST make sure that all the vacuum hoses are properly connected and none of them is leaking due to, perhaps, cracks in a dried out vacuum hose. That's basic stuff that has to be verified before going off the deep end and over-diagnosing this problem.
Always verifiy the basic things first. I wish I had a dollar for everytime someone has posted about a problem, we'd all spend days suggesting things to check (some even recommend changing certain parts) ONLY to find that the guy had failed to check a very BASIC thing which turned out to be the cause.
The Devil's in the Details.
Keep us posted.
Jake
