1999 Mustang GT. new IAC valve and continues to idle from 500-1000. PLEASE HELP - Page 2 - Ford Mustang Forum
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post #16 of 24 (permalink) Old 03-09-2010 Thread Starter
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Ok so I have taken my car to Ford and had them run a dignostic. They told me that the reason for the idle issue is that my battery and altinator failed the tests that they ran them through. So along with the lack of juice flowing, I also have performance pullies and an audio system,(Amp,sub,aftermarket speakers and deck) that they said will continue to drain more and more from the car. OK... the audio system I can understand, but how would the pullies come into play? And finally they also told me that they pulled my Mass Air Intake valve and cleaned it. They told me that it had a small amount of carbon build up and that the idle issue was resolved, but they didnt fix anything!!! And they also said that it could be the fuel pump losing preasure because I noticed that when I really get on it... and I mean GET ON IT, when I come to a stop it just slowly and steadly idles down untill it dies. Its done this to me twice now, the weird thing is that it starts right back up no problem. Any advice on what to do from here would be awesome. Thanks
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Idles from 500-1000? Do you mean it has a rolling idle? Like continuosly fluctuates?

As far as vacuum leaks go, brake clean can answer that, spray around your intake gaskets: no rpm change, no leaking intake gaskets. Look at all your rubber hoses, thoroughly!

Disconnect the battery, IAC, and PCM; White/Light blue wire from IAC to Pin 83 on the PCM can be tested for resistance, Fuse 2 (20a) to Red wire to IAC can be tested for resistance. That gives you your IAC circuit. Usually if you unplug your IAC while it's running, the car should die (try it a couple times).

To be SURE on the computer reset, do half an hour on the battery disconnect if you decide to do it.

As far as the EGR goes, it's not designed to run at idle. Usually it's off idle on cruise, maybe even acceleration.

90 Hatch - "The Purple Project"
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Well, they're full of ****. The battery might've failed the "Load test", and the alternator might not be putting out the specified amps. The idle issue is a driveability concern. Unless they can prove it, don't believe it. The pullies; Think of a mountain bike...Gear ratios, cept with pullies. The stock Crank pulley is designed to spin the pullies more revolutions than the "performance pulley" you replaced it with. For the hp gain you think you got...Go back to the stock one. You spin your alternator less=less charging ability (no bueno), you spin your waterpump less=less cooling ability (no bueno), you spin your a/c compressor less=less cooled air blowing in your girlfriends face when she's all prettied up to go out in the summer. Please, just put the stock one back on...
You don't have a mass air intake valve. You have a MASS AIR FLOW SENSOR, and an IDLE AIR CONTROL VALVE. So did they fix your idle concern by cleaning the MAF? If they did, they DID fix something..(your idle concern) If not, does your car still have a rolling idle?

90 Hatch - "The Purple Project"
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post #19 of 24 (permalink) Old 03-13-2010 Thread Starter
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TxTomcat07...WOW, that is a lot of info! So ya I meant to put mass air flow sensor not the valve. And no the idle issue was not fixed. As far as a rolling idle fluctuation, it only idles from 500-1000 when I am stopped. And as far as pullies go..... I need to buy another factory one because I dont have the original. So I will continue to check on hoses for leaks, and I have also messed around with the IAC plugging and unplugging as well as removing while the car is on and ya it does die. The down side to resetting the computer in my whip is that when I took it to Ford they told me that someone had cleard the codes which I had obviously done and that they were unable to find out any info because of that
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Did you get this problem resolved? My '99 GT does this ONLY when the A/C is on - also replaced IAC no change. Suspect problem with A/C.

Black 1999 Ford Mustang Gt, Steeda cold air intake, Flowmaster Cat-back with Magnaflow Tru-X X-Pipe, Steeda Progressive springs, Adjustable camber plates, lowered 1 1/2 inches, 3:73 Rear, Aluminum Driveshaft, Steeda shifter plate, Stage 1 Luk Pro Gold Clutch, Sub-Frame Connectors, Mach 1 Grill delete, Mach 1 Chin Spoiler, Steeda Rear Deck Spoiler, Ford Racing Pedals, possibly a Predator tune?
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Dyno- 241.9 rwhp
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post #21 of 24 (permalink) Old 05-01-2010 Thread Starter
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No I have yet to resolve this issue. The car has not died on me again but still continues to idle like a ratard!! I am kind of short on money at this time because I keep buying other stupid crap, so I have yet to put a new altinator and batt even though that may not be the issue per tomcat.
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I have the exact same problem on my 1999 GT and have been reading up on it. On another thread a guy solved the problem by changing the freon (see http://www.allfordmustangs.com/forum...ems-wierd.html) which apparently provides lubrication.
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post #23 of 24 (permalink) Old 05-12-2010 Thread Starter
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Well I know its not my AC because it seems like when I turn it on, the car idles fine. Almost as if when the AC is pulling the extra power the altinator has to actually do its job,,, I noticed that the other day now that its getting warmer. I have a sneaking suspicion that it may be my intake manifold gasket because when I got the car I noticed it was leaking just a bit from around that area right in front of the fire wall, so I cant visually confirm. Anyway I bought of stuff from autozone thats supposed to stop that from happening basically just seal up the cracks. Well I havent noticed any more leaks but the car is still doing its crazy Idle crap!
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I was having the same issues with my 2003 GT and just got it fixed yesterday... forced a loud rumble from my air box also. took it to my local shop and they ended up switching out the IAC valve.

They tried using a generic 3rd party one first and that made it worse, swap it out to a Real Motorcraft, did the battery ECU reset, and swapped out a new Fuel Filter. I Got 82K miles on the car.

One rule i learned with this car, If they still make a Motorcraft part, Buy it instead of trying to save cash. Ford Electrical parts are very Picky.
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