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Old 09-17-2013, 08:13 PM   #1
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Need help with rough idle!!!

What's up guys!!

One of my best friends has an 02 mustang GT.
He bought the car knowing it wasn't 100% great
It was a v8 running on 3 cylinders(metaphorically speaking)
The previous owner didn't take care of it at all! Lol

We fixed it up, replaced the spark plugs, and alternator and it'd run fine.
We replaced all the fluids and filters ran like a champ

Last week he started having a rough idle.
So I took out his MAF and cleaned it, along with his IAC valve

It ran good, idles normal.
However, whenever he gets on it and ten comes to a stop, it'll have that rough idle.
Any idea on what it might be?
Any and all help is appreciated!
Thanks!!!

A couple pics of his car :p
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Old 09-17-2013, 08:20 PM   #2
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IAC can always be an issue so good to know I checked that. Could be a clogged or faulty injector? See if u can pin point if there is a mis somewhere or if its just rough in general. Also check spark plug gaps and the coil on plug boots. Plus some the car has not been maintained well since he got it check all the vac lines Amy cracks can cause issues. Take some carb cleaner and spray around all the vac lines with the engine running. If the idle changes then there's a leak somewhere. Hope this info is helpful.
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Old 09-17-2013, 08:24 PM   #3
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Quote:
Originally Posted by jhherndon View Post
IAC can always be an issue so good to know I checked that. Could be a clogged or faulty injector? See if u can pin point if there is a mis somewhere or if its just rough in general. Also check spark plug gaps and the coil on plug boots. Plus some the car has not been maintained well since he got it check all the vac lines Amy cracks can cause issues. Take some carb cleaner and spray around all the vac lines with the engine running. If the idle changes then there's a leak somewhere. Hope this info is helpful.
I replaced the spark plugs about a month ago, and they were gapped correctly.
And how would I check the coils?

---------- Post added at 08:24 PM ---------- Previous post was at 08:21 PM ----------

And how would I check a cloves or faulty injector :p
I apologize for my lack of knowledge XD
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Old 09-17-2013, 08:43 PM   #4
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Has the car been checked for codes?

Im sensing a failing oxygen sensor on this one.

Ive already been wrong once today though so take that for what it's worth... lol
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Old 09-17-2013, 08:53 PM   #5
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Has the car been checked for codes?

Im sensing a failing oxygen sensor on this one.

Ive already been wrong once today though so take that for what it's worth... lol
It's not throwing any codes, it had a cam positioning sensor, but that was because of a bad altwrnator

---------- Post added at 08:53 PM ---------- Previous post was at 08:50 PM ----------

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It's not throwing any codes, it had a cam positioning sensor, but that was because of a bad altwrnator
Which we replaced, so it's no longer there :p
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Old 09-17-2013, 09:23 PM   #6
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If its not showing any codes it's prob me a Mis with the coil packs or injectors. When I had the issue it threw a code so I swapped the injector with the code to a diff cylinder and it showed up there so I knew my problem. Doesn't mean they may not be a little dirty though. Lucas injector cleaner and some 93 octane can help with that. As for the sensor from stray bullit it's a good point. All of that stuff works together and if one goes it screws with everything. I'm sure some other guys on here have had some issues so they will chime in. On a positive note all of these little rough idle issues aw relatively minor in most cases. It's just figuring it out that's the hard part.
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Old 09-17-2013, 09:34 PM   #7
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If its not showing any codes it's prob me a Mis with the coil packs or injectors. When I had the issue it threw a code so I swapped the injector with the code to a diff cylinder and it showed up there so I knew my problem. Doesn't mean they may not be a little dirty though. Lucas injector cleaner and some 93 octane can help with that. As for the sensor from stray bullit it's a good point. All of that stuff works together and if one goes it screws with everything. I'm sure some other guys on here have had some issues so they will chime in. On a positive note all of these little rough idle issues aw relatively minor in most cases. It's just figuring it out that's the hard part.
Okay, but if its not showing any codes... How would I know XD

---------- Post added at 09:33 PM ---------- Previous post was at 09:32 PM ----------

Just talked to him, he used fuel injector cleaner 2 weeks ago, an he's used 93 since he bought it

---------- Post added at 09:34 PM ---------- Previous post was at 09:33 PM ----------

My gut is telling me it's a bad vacuum hose

Which seem the most susceptible to cracking?
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Old 09-17-2013, 09:42 PM   #8
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Okay, but if its not showing any codes... How would I know XD

---------- Post added at 09:33 PM ---------- Previous post was at 09:32 PM ----------

Just talked to him, he used fuel injector cleaner 2 weeks ago, an he's used 93 since he bought it

---------- Post added at 09:34 PM ---------- Previous post was at 09:33 PM ----------

My gut is telling me it's a bad vacuum hose

Which seem the most susceptible to cracking?
All of them...

Like JH said it could be any number of small things.
Don't rule anything out

There can be codes without the CEL ever coming on.
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Old 09-17-2013, 09:47 PM   #9
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All of them...

Like JH said it could be any number of small things.
Don't rule anything out

There can be codes without the CEL ever coming on.
Well in that case I'll tell him Togo scan it and see I it comes up with anything
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Old 09-17-2013, 09:49 PM   #10
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