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Solving idle problems part 1 - Cleaning your IAC
Does your idle rise and fall over and over again? Does your 'Stang stall when you come to a stop, or even when you put it in gear? Well if so then this series of articles is for you.
In this age of fuel injection, idle problems can literally be caused by hundreds of different things. What this series of articles is aimed at is how to fix the most common idle problems found in the Mustang.
The fuel injected Mustang uses a small motor/valve assembly that allows a specific amount of air to enter the engine to control it's idle. This valve is comonly called the idle motor, the IAC (idle air control) or the IAB (Idle air bypass). When your car is new the IAC works remarkably well. The problem arises when the car gets some miles on it (usually 75K+) and carbon fouling takes its toll.
What happens is dirt, excess air filter oil, and most notably carbon gunks up the IAC valve and doesn't allow it to either open or close properly. This can cause an really high idle, a lumpy/surging idle or no idle at all. The solution is to either replace or clean the IAC. Obviously we are going to do the later and here is how.

1. What is needed?
- 8mm or 5/16 socket and ratchet
- Can of Carburetor/throttle body cleaner

2. Locating the IAC valve:
Depending on the year of your Mustang the IAC can be in a few different locations.
- On 5.0L Fox body cars the IAC is bolted to the side of the throttle body.
- On SN-95 cars it is bolted to the intake manifold
- On 4.6L DOHC and SOHC engines the IAC is located on the upper intake manifold.
In reality once you know what one looks like (picture 2 "B" from a 94-95, fox body's have longer silver IACs) you should have no trouble finding yours. They all look basically the same except pre-94 cars were made of metal and are silver, 94-up cars are black plastic.
Mustang IAC location
Picture 1

3. Removing the IAC:
This part, like the rest of the steps in this article, is simple. The IAC has an electrical plug that needs to be disconnected (picture 2 "C") Then all you have to do is remove the two 8mm-5/16" bolts (Picture 2 "A") that hold the IAC to the throttle body or intake. Watch out for the IAC motor to throttle body gasket, don't lose it!
Mustang throttle body with IAC
Picture 2

4. Cleaning:
Next all you do is use the carb cleaner to clean the carbon out of both of the holes (picture 3 "C") in the IAC valve and both of the holes in the intake/throttle body.
Mustang IAC
Picture 3

5. Putting it back together:
Yet another self explanatory step. Put the IAC in place and install/tighten the 8mm bolts. Make sure you don't forget to reinstall the gasket.

6. Fire her up!
Finally you need to start the car and let it run for a few minutes to burn any leftover carb cleaner in the intake. You may have to crank the engine a little more than normal to start it for the first time and don't worry about the white puff of smoke you see coming from the exhaust because again it's just the carb cleaner.

Check out part 2 - The throttle body


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your car or to yourself while working on your car. You work on your car at your
own risk. If you don't know you can do this yourself, bring it to a mechanic who can.
Any modifications, repairs or maintenance can be very dangerous, so be careful!