sweetbeats

Greetings folks...first post.

I recently kind of adopted a 2001 Mustang GT with the 4.6L V8, about 56,000 miles on the clock, and a Vortech HO supercharger kit with Maxflow cooler under the hood and all kinds of Kenny Brown chassis goodies.

I have a pretty extensive background in electronics as well as mechanical maintenance (have done my own engine rebuilds, etc.), so I'm hoping I can tackle this issue myself, but before I go wandering off in the wrong direction I wanted to consult with experienced owners here as this is my first Ford V8.

There is a problem with the idle consistency. Sometimes it idles at 2000rpm, other times it won't hold idle and dies when the engine is warm, shut off and restarted. Then again other times it will idle at 1500rpm, like when I've been driving and pull up to a light...once I come to a stop sometimes I can get it to settle to 700-800rpm if I shut off the interior heating/cooling system and wait patiently.

Is there an idle governor that goes bad on these engines? Other ideas? Something more complex?

I have a service manual by the way.

I should also probably mention there is also a primitive programmer of sorts installed (the kind you interface over a serial port with a computer) to manage at least the ignition system...maybe fuel management too? Not sure how sophisticated the injection system is on these engines. Other than the idle issue though this pony runs fantastic. It has the 5-speed and it is the coolest sounding car *ever*, and will knock you back in the seat whenever you want...gets about 17mpg too. Last dyno test when the engine was tuned resulted in over 300hp at the wheels.

jwog666

idle air control motor is used to control idle, but with all the mods that have been done to the car, it could be that the previous owner didnt install something correctly, or it could be that you have a failed or faulty IAC, ECT, MAF. you will need a scan tool that will allow you to monitor sensor data in order to diagnose this. good luck

sweetbeats

Thanks for the reply. Does the idle air control motor control air flow Upstream from the intake manifold?

I'll start by studying on that system, and also exercising and inspecting all electrical connections in the engine compartment and to the programmer.

My assessment is that the previous owner did a nice job of installation, but I also realize once its been modded, especially with the nature of the mods that have been done, all bets are off.

jwog666

the IAC is after the throttle plate, and on factory setups will be on he upper plenum elbow

sweetbeats

So the next time the idle was acting up I popped the hood and pulled the connector from the device in pointing to in the picture below, which I believe is the IAC motor. Am I correct? The idle immediately settled down to where it should be. Plugged back in and the idle bumped up...pulled it again and it settled down. What does this mean? Bad motor, inappropriate messages going to the motor?

jwog666

check for vacuum leaks, iac will only raise idle when directed by the pcm, and its not stuck, because when u unplugged it it idled down, check all vac lines and pcv connections, basically everything between the maf and the cylinder head for leaks need to be check to make sure that there are no vacuum leaks

sweetbeats

Excellent. Makes sense. I'll check things out and report back.

swarthyfellow

sounds like the IAC is just sticking , just spraying some carb cleaner thru it and put it back on. I used to have to do this every 10K or so but i haven't in the last 30k or so. Also, might be worth checking where the throttle plate itself is. Looking thru the throttle body there should just be a tiny light gap when its close.

sweetbeats

But if that's the case, wouldn't there be no change when I unplugged the IAC with the engine running?

sweetbeats

FYI the car is fitted with a Zone-5 Performance Products SHM MAFterburner and a BBK 78mm throttle body. I'm having trouble finding any info on the MAFterburner though I have a CD-ROM disc and interface cable.