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ok so ive searched on google and have found threads about this but none seem to describe it like my problem so ill just start a new thread and if someone will help by answering or sending me to a correct thread i would greatly appreciate it cause the ford dealership here isnt so great LOL.....when i have problems i rely on the internet and other mustang owners to figure it out NOT the ford mechanics........so heres my problem...all u guys who drive 5 spd 99-04 gts should have noticed when u come up to a stop in neutral right when or before u COMPLETELY stop the rpms kick down right? mine will be around 1500rpm when im coming to the stop in neutral and right when or before i completely stop theyll kick down to like 650rpm and stay there.....i was told ford made them do this...something transmission related?......well now when my car does that instead off kicking down to 650 smoothly it will kick down then up then down then up then down then up really fast...it sounds kind of like a high idling cam when it does it....thats about the best way to describe the sound and sometimes it will sputter like that for just a sec and somethimes it lasts like 3 or 4 seconds then it will kick all the way down to like 4 or 500rpm and almost die then idles smoothly....its been doing this for about a month now and i have no idea what that could be it doesnt do it every time and it ONLY does it when i come to a stop in neutral
 

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I would start by checking out the Idle Air Control Valve, and the Throttle Position Sensor. While you are in there I would also look around and make sure you don't have any vacuum leaks. particularly where the IAC connects to the intake piping, and where the pcv valves connect to the plenum.
 

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I circled the TPS and IAC in red. You can also check the vacuum lines I traced in yellow. You also might want to make sure that your intake is connected good at the throttle body and the MAF.
 

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Discussion Starter #4
I would start by checking out the Idle Air Control Valve, and the Throttle Position Sensor. While you are in there I would also look around and make sure you don't have any vacuum leaks. particularly where the IAC connects to the intake piping, and where the pcv valves connect to the plenum.
ok thanks ill check it out in the morning.....i was planning on cleaning the iac within the next few days cause what i had read from all the other threads was that it was probably the problem
 

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Airmandavis,

How do you check the vacumm lines. Yeah I'm new to engines, but have been putzing around on mine and actually fixed my rough idle issue last month, but it's back. I cleaned the MAF and it fixed the issue , but now check engine light is back on.

I am getting the codes for "MAF low inpur circuit" and "Fuel rail pressure sensor malfunction:

Thanks
 

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I always visually inspect them for cracks or cuts, then make sure they are well attached. You can also take a can of carb cleaner or a propane torch(unlit of course) and spray along the suspect area if you hear the engine start to stumble you have found your problem.
 

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Discussion Starter #10
well i cleaned the iac yesterday and it didnt do the rough idle thing but this morning when i got in it it did it the first time i came to a stop.....guess ill just get a new one and see if it makes it better...vaccum lines are brand new btw
 

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I had the same issue it sounds like and cleaning my iac helped. I would say if it helped initially, then the issue came back, try replacing it.
 

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sure sounds like an iac issue.
 

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you could also try checking your coils and coil pigtails, the connectors can get brittle over the years.if it doesnt seem to run as good as you think it should while youre cruisin around it could be that,happened to me before, when i would come to a stop idle would drop and feel like it almost was going to die out,cruisin was ok just felt a lil weak,here one of my coil connectors was snapped and wasnt gettin a good connection,just had to replace the pigtail,pretty easy to check so maybe worth a shot.
 
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