Manual Control Over IAC?

Terrorist 5.0

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Hi everyone. Everyone knows about the rev hang in these cars between shifts. For some people, this feels normal. But for me, it was unbearable, especially since I learned to drive on older (some carbed) cars. To remedy this, I unplugged the IAC. The car drives amazing now, but cold starts are a little interesting. The car runs really rich because of the lack of air from the IAC, and likes to surge and stall unless I pedal it for sometimes a second or two, to a full minute or more at times. I have a new IAC on the car already from when I tried the IAC restrictor plate (which didn't work), and I think it should be put to use. Has anybody ever wired in a manual control for the IAC? I only need it to be on/off (it is pulse width modulated if I am not mistaken so I should really be saying 100/0% duty cycle), just so I can have a somewhat peaceful cold start instead of pedaling it. If anybody has done that, please explain what you did, or if nobody has done it, please feel free to spitball some ideas. I would love to hear it.
 

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not sure how far into the build you are but a tune is how it should be fixed. If it is done right it would fix the rev hang and increase your driveability of it and you might gain a little power as well.
 

96blak54

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Any deviation from stock parts, like a bigger aftermarket throttle body. The stock tune is doing what its suppose to do and the bigger throttle body is allowing more air to pass through, although its closed, its bigger area still allows more to pass though. A tune will definitely correct it
 

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While i'm on the "fix it right" bandwagon, you could wire in a time-delay relay that disconnects the IAC from power after startup. Say 5 mins or so. Downside is this would happen every time you start the car so even with warm you'll need to live with it for a few mins.
 

ttocs

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I forgot to mention that when I say get a tune, I am not saying go to american muscle and get a bama tune. There are better options depending on the budget.
 
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As far as the car goes right now, it is completely stock, apart from some suspension work the previous owner did (which I will correct sometime soon), I am not planning to touch the engine anytime soon other than maybe an under drive pulley, and the only other mod going in the car is 3.31 gears. The drivability of the car is very good so long as it has warmed up some, it’s mostly on startup (mostly cold but hot too) that the car runs rich (which I believe to be due to the absence of air from the IAC). I don’t really want to get a tune and mess with the car too much, I just want to be able to have the IAC hold me at a slightly higher RPM when starting for a couple minutes in the morning. Ideally, I would imagine a small switch with a low, medium, and high setting, say for 900, 1200, and 1500 RPM, although one setting would be easier.
 

Mustang5L5

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i think you have other issues that need to be addressed.

If you are running rich, this is not due to the IAC. The IAC just bypasses air around the throttle blade, but all that air has been passed through the MAF so it is accounted for. Whether it goes through the IAC or not doesn't matter.

Have you dumped codes? Checked for vacuum leaks? The 5.0's tend to be very sensitive to vac leaks and I would bet this might be your issue instead of the IAC.

I have a modified 5.0 and do not have any sort of hanging idle between shifts, and my car is still untuned.
 
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Terrorist 5.0

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i think you have other issues that need to be addressed.

If you are running rich, this is not due to the IAC. The IAC just bypasses air around the throttle blade, but all that air has been passed through the MAF so it is accounted for. Whether it goes through the IAC or not doesn't matter.

Have you dumped codes? Checked for vacuum leaks? The 5.0's tend to be very sensitive to vac leaks and I would bet this might be your issue instead of the IAC.

I have a modified 5.0 and do not have any sort of hanging idle between shifts, and my car is still untuned.
I have no codes relating to fuel supply, I only have one for EGR which was blocked off by the previous owner and for the idle being mechanically too high (to compensate for lack of IAC), the car has no vacuum leaks (smoke tested). The sensors relating to starting are new and seem to be in spec according to my meter, which leads me to believe the only other reason the car smells of gas and sputters is that the ECU just enriches the AFR during startup, and relies on the IAC to counteract/modulate idle. This may be completely wrong, but when I had the IAC connected, the car didn’t surge as it fought itself to stay alive, and it didn’t smell nearly as strong. This is mostly my theory on the matter and may hold no truth, but regardless, having control of the IAC would definitely help out if not eliminate the relatively minor inconvenience I am having while not dealing with the pesky rev hang. By the way, you mentioned you didn’t have any rev hang. Is your Mustang an SN95 as well? AFAIK, the Foxes do not have the rev hang feature. I should also mention that I have lowered the idle to the standard setting to eliminate the code but the problem persists.
 

ttocs

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do a smoke check for vac leaks when it is cold. If you don't smoke just invite one of your friends over that does to help out. He can blow the smoke in the vac line that goes to the brake booster and you can look for the smoke.
 

lwarrior1016

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I’m not sure if you are going to be able to control the IAC like that. Being that it is ground PWM. It may need to see a pulse ground to make the pint or move, I’m not sure if constant ground will do it.

The valve should get 12v key on power, and then ground is regulated. You could pull the valve off, turn the key on and send the pwm wire straight to ground to see if it moves the pintle.
 

ttocs

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I know I had to, and a lot of others with holley systems have switched to an LS based IAC as the holleys do not like the ford system. You could do this if you needed but I would start with a simple smoke check or just start replacing all the rubber vac lines that look original as they are probaby leaking.
 

lwarrior1016

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I know I had to, and a lot of others with holley systems have switched to an LS based IAC as the holleys do not like the ford system. You could do this if you needed but I would start with a simple smoke check or just start replacing all the rubber vac lines that look original as they are probaby leaking.
He’s got a factory computer though, it won’t control a stepper IAC.
 

ttocs

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sorry I thought he mentioned he was going to make his own controller somehow maybe ardiuno based or something. Idunno.
 
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Terrorist 5.0

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sorry I thought he mentioned he was going to make his own controller somehow maybe ardiuno based or something. Idunno.
I am going to be making my own controller. In fact, the last thing I want is the ECU controlling the IAC and hanging the RPM’s as I shift.
 
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Terrorist 5.0

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I know I had to, and a lot of others with holley systems have switched to an LS based IAC as the holleys do not like the ford system. You could do this if you needed but I would start with a simple smoke check or just start replacing all the rubber vac lines that look original as they are probaby leaking.
Please tell me more about the LS based IAC modification you are talking about. I am open to any ideas. If it really is a stepper, I would imagine it is a lot easier to control than a PWM motor.
 
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Terrorist 5.0

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I’m not sure if you are going to be able to control the IAC like that. Being that it is ground PWM. It may need to see a pulse ground to make the pint or move, I’m not sure if constant ground will do it.

The valve should get 12v key on power, and then ground is regulated. You could pull the valve off, turn the key on and send the pwm wire straight to ground to see if it moves the pintle.
I will try sending the wire to ground and monitoring the IAC sometime soon, maybe tomorrow after work. I will report back with what happens. I imagine it will max out the IAC, seeing that more duty cycle in this application should mean more ground. If I’m not wrong, a constant ground should be similar to maxing the duty cycle, opening the IAC all the way. Then again though, I am more of a backyard electrician, with my backyard resembling a GTA Online lobby worth of chaos. Here’s to hoping.
 

ttocs

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the ls system is a little different but it is still pwm. Building your own is not going to be as easy as just flipping a switch and everything is good.

Any chance you checked the charcoal canister in the pass fender while you were doing the smoke check? It is a common point for leaks to happen and a smoke check might not show up with its location keeping the smoke in the back of the fender while you are concentrating under the hood. You would need to remove the wheel and the inner fender to see it.
 

lwarrior1016

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The LS sensor is not pwm, it is a stepper motor. It is a 4wire system and the controller/computer tells it how many steps to move away, to allow more airflow.
 

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