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Hello, my 2003 Mustang gt began idling at over 2000rpm on my drive home from work the other night. I checked the TPS and it was working properly so i checked for vacuum leaks and found nothing. I then took the IAC off and cleaned it thoroughly and popped it back in. The car went back to normal idle after that so i thought i was golden. But after a few minutes i started it back up and it was back up at a 2000-2500rpm idle. I went to autozone and got a new IAC for it and put it on. After that the car would stall out right after starting. I feathered the gas pedal and got it to idle but now it idles between 650-800rpm. When put into gear (automatic) it will drop down to nearly 500rpm and stall out. I went back and checked over everything and found no vacuum leaks or any obvious signs that would cause this. I have fiddled with it all day and i'm out of ideas. I did fill my tank right a few hours before it started at my normal gas station, could it be bad fuel? Also there is no Check Engine Light. Any insight will be appreciated, THanks!
 

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How many miles on the car? Get an OEM IAC, the aftermarket IAC are pretty much hit and miss, many have problems with them. Did you replace the gasket as well? How long ago since you replaced the fuel filter? A tune-up (spark plugs, air filter, fuel filter) often solves problems like that when the engine stalls out. My bets are on a faulty IAC though, but a tune-up never hurts if it has been a few years.
 

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Does the original IAC have the black vent? What about the replacement?

Did you disconnect the battery during the work? If so, this could be the source of the low idle as the PCM re-learns new idle trim values.

If the low idle continues start by looking for a vacuum leak between the MAF and throttle body.

Here's some more information on how to trouble shoot.

http://www.allfordmustangs.com/foru...ng-idle-idling-rough-post2260649.html#2260649

Just wondering how you confirmed that your TPS was working correctly?
 

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How many miles on the car? Get an OEM IAC, the aftermarket IAC are pretty much hit and miss, many have problems with them. Did you replace the gasket as well? How long ago since you replaced the fuel filter? A tune-up (spark plugs, air filter, fuel filter) often solves problems like that when the engine stalls out. My bets are on a faulty IAC though, but a tune-up never hurts if it has been a few years.
the car has 99,377 miles on it. ANd yes i put the new gasket on with the IAC, however i havent messed with the fuel filter at all yet.
 

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Discussion Starter #5
Does the original IAC have the black vent? What about the replacement?

Did you disconnect the battery during the work? If so, this could be the source of the low idle as the PCM re-learns new idle trim values.

If the low idle continues start by looking for a vacuum leak between the MAF and throttle body.

Here's some more information on how to trouble shoot.

http://www.allfordmustangs.com/foru...ng-idle-idling-rough-post2260649.html#2260649

Just wondering how you confirmed that your TPS was working correctly?
Not sure about the "black vent", would that be the black gasket?

I DID disconnect the battery for well over 15 minutes after replacing it. Even disconnected it overnight (about 12 hours) and the idle seemed a little better (800-900) but then stalled in gear when applying gas.

Also i took a TPS off another '03 and switched them and mine was still idling rough and the other ran just fine so i figured it wasnt the TPS. Not sure how reliable of a test that is though.
 

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the car has 99,377 miles on it. ANd yes i put the new gasket on with the IAC, however i havent messed with the fuel filter at all yet.
If you don't know how long it has been since last time the fuel filter was changed, I would recommend changing it regardless. It is one of those things that is nice to know has been replaced recently, so you don't have to worry about it for years to come.
 

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Discussion Starter #7
If you don't know how long it has been since last time the fuel filter was changed, I would recommend changing it regardless. It is one of those things that is nice to know has been replaced recently, so you don't have to worry about it for years to come.
After a tune up and replacing the fuel filter the car seems to idle a tad better but still idles too low when coasting or braking and stalls out. Im all out of ideas.
 

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Does the speedometer work?

Has the battery been confirmed to hold a charge? Are the battery terminals CLEAN and tight?

Does the cluster gauge "sweep" sometimes at key on?

What is the hot idle in Park? In Drive?

Does it mainly die while coming to a stop in drive? If so, the problem may be the lock up torque converter not releasing as it should.
 

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Discussion Starter #9
Does the speedometer work?

Has the battery been confirmed to hold a charge? Are the battery terminals CLEAN and tight?

Does the cluster gauge "sweep" sometimes at key on?

What is the hot idle in Park? In Drive?

Does it mainly die while coming to a stop in drive? If so, the problem may be the lock up torque converter not releasing as it should.
Battery is new and clean so I could rule that out.

Gauge cluster seems to be acting normal

Idle in park is 1000 and in gear it drops to anywhere from 500-700

While braking hard or for a long period of time is when it dips way down under 1000 and stalls out. Today I noticed it would drop way down but as I stopped it would shoot back up to 500-700rpm.
 

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Discussion Starter #10
Battery is new and clean so I could rule that out.

Gauge cluster seems to be acting normal

Idle in park is 1000 and in gear it drops to anywhere from 500-700

While braking hard or for a long period of time is when it dips way down under 1000 and stalls out. Today I noticed it would drop way down but as I stopped it would shoot back up to 500-700rpm.
**oh and yes the speedo works
 
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