Won't idle down
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8th Gear
Joined: Aug 2011
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Won't idle down
Yesterday 09:06 PM14Kevman
I have a 85 tune port with 27k for miles I have a intermittent problem the car won't idle down below 15-1600 when this happens and it's getting to happen more often the 4+3 overdrive kicks on and off on its own were should I start??
I have a 85 tune port with 27k for miles I have a intermittent problem the car won't idle down below 15-1600 when this happens and it's getting to happen more often the 4+3 overdrive kicks on and off on its own were should I start??
Advanced
Joined: Oct 2014
Posts: 94
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From: Tampa
Clean the throttle body, and IAC motor (and its housing).
Thread Starter
8th Gear
Joined: Aug 2011
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Team Owner
Joined: Jul 2004
Posts: 28,471
Likes: 3,290
From: Hartford WI
If we see that there is a high idle problem, we can attack it better. So if your IAC 0 counts and you turn the screw out and still 0, you have a leak somewhere and the ECM is compensating normally but sometimes will not compensate if it is out of the window hence the high idle.
Le Mans Master
Joined: Feb 2005
Posts: 6,481
Likes: 566
From: Clearwater Florida
..... Try lubing the throttle shaft in the throttle body by spraying it with a silicone or Teflon based penetrating lubricant ... spray in the 3 places where the throttle shaft passes through the throttle body . Do this while rotating the throttle by hand ... engine off please ... the overdrive operation is controlled by the ECM not by vacuum ... Also check for vacuum leaks .....
Last edited by C409; Apr 23, 2017 at 12:23 PM.
Oil Producer
Joined: Apr 2014
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yes it is possible that the high idle can cause the overdrive to cycle. Here is the logic: (i think. others please chime in)
ECM requires closed loop to enable overdrive.
large vacuum leak, whether that is a defective stuck open IAC valve or a rotted hose for a faulty EGR diaphragm or a leaking brake booster check valve or a compromised intake manifold gasket.... create a condition where your O2 sensor sees a higher air to fuel ratio and causes injectors to dump more fuel in, which evens out the air to fuel ratio but causes the car to run poorly which kicks the car out of closed loop, which forces the disengagement of the overdrive unit
everything is so interconnected that as aklim says it is important to see which sensors are with you and operating specs and which ones are not.
you may in fact have more than one thing happening. You may have a massive vacuum leak, and you may have a sensor that is required to maintain close to the operation that is on the fritz. But this situation is definitely on the table where your huge vacuum leak could be the cause of everything.
ECM requires closed loop to enable overdrive.
large vacuum leak, whether that is a defective stuck open IAC valve or a rotted hose for a faulty EGR diaphragm or a leaking brake booster check valve or a compromised intake manifold gasket.... create a condition where your O2 sensor sees a higher air to fuel ratio and causes injectors to dump more fuel in, which evens out the air to fuel ratio but causes the car to run poorly which kicks the car out of closed loop, which forces the disengagement of the overdrive unit
everything is so interconnected that as aklim says it is important to see which sensors are with you and operating specs and which ones are not.
you may in fact have more than one thing happening. You may have a massive vacuum leak, and you may have a sensor that is required to maintain close to the operation that is on the fritz. But this situation is definitely on the table where your huge vacuum leak could be the cause of everything.
you may be able to find someone locally with an ALDL scanner. if not, and you own a laptop, you can buy the AL DL cable and download to your pro RT, learn how to use it, and read your own sensors.Sorry to add more complexity but being as you have a 1985, this particular year will not let itself be scanned in the same way that 1986 and later years allow itself to be scared. What Imean is for 1985 the only way that the computer will let itself be scanned, or observed, is while it is holding something called a field test mode. Which forces the car to do many things, one of them is holding the idle at 1000 RPM. Normally I see threads like this where a person's idle is surging back-and-forth from 400 RPM up to 1000 RPM and unfortunately one cannot view the IAC position as aklim has recommended with the 1985 computer. What happens is as soon as you try to observe it the IAC is repositioned by the ECM to hold a 1000 RPM. Sort of like quantum particles where once you try to observe them they change so you can never actually see them in the state you want to see them!However, and again sorry for the complication, in your particular circumstance I think it will work! Your idol is consistently above 1000 RPM. So at a minimum you should be able to see that your IAC is being pushed into the zero position even though it is aiming for 1000rpm and holding it. That would verify you have A vacuum leak somewhere else!
personally, my advice is to go through the minimum Idle procedure right now, do a Google search for it, while you are waiting for your scanning system to be available to you. It is possible that someone messed with your throttlebody blades so bad using the screw that even at a zero IAC you are holding a very high rpm. If that's all it is, The minimum idol procedure will fix it. ak doesnt like to recommend that procedure because if the IAC valve is faulty it won't work. I agree with him. But this is something you could do and it takes about 5 minutes while you are waiting for the scanning system to arrive. The second thing you could do while you're waiting, is as the poster above said, look for vacuum leaks. Chances are, it's a vacuum leak. I get in there with a can of brake clean or WD-40 or something that is flammable and I spray until I hear an RPM increase.
again, sorry for the complex reply but hey these are complex machines!
personally, my advice is to go through the minimum Idle procedure right now, do a Google search for it, while you are waiting for your scanning system to be available to you. It is possible that someone messed with your throttlebody blades so bad using the screw that even at a zero IAC you are holding a very high rpm. If that's all it is, The minimum idol procedure will fix it. ak doesnt like to recommend that procedure because if the IAC valve is faulty it won't work. I agree with him. But this is something you could do and it takes about 5 minutes while you are waiting for the scanning system to arrive. The second thing you could do while you're waiting, is as the poster above said, look for vacuum leaks. Chances are, it's a vacuum leak. I get in there with a can of brake clean or WD-40 or something that is flammable and I spray until I hear an RPM increase.
again, sorry for the complex reply but hey these are complex machines!
Last edited by VikingTrad3r; Apr 23, 2017 at 01:05 PM. Reason: siri really bad on this one lol.
Le Mans Master
Joined: Feb 2005
Posts: 6,481
Likes: 566
From: Clearwater Florida
..... If the throttle shaft is sticking open , it will hold the TPS at a value above idle . The load will change depending on road speed and gear position and braking . All causing the ECM to "think" that you're driving the car this way .....
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