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Old 07-13-2014, 02:41 PM   #1
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Misfiring

My 03 gt started misfiring in cylinder 3 about a week ago so I replaced the spark plug and all was fine. Just a few days ago, cylinder 1 started misfiring terribly and was unpleasant to drive. Now it isn't missing as bad but it idles a little rough and feels like it has no power (I used to be able to chirp tires when I floored it). Anyone know what could be up?
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Old 07-13-2014, 03:30 PM   #2
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When you say "replaced the spark plug", do you mean that you only replaced that one spark plug or did you do all eight?
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Old 07-13-2014, 03:41 PM   #3
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I only replaced that one. I ha previously checked all of the plugs and they looked fine.
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Old 07-13-2014, 03:43 PM   #4
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At idle, the rpms fluctuate between 500-1000 rpms as well. Any ideas? Seriously feels like a loss of power
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Old 07-13-2014, 03:50 PM   #5
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Hmmm.
Ok. They are normally changed in sets though...
If you're comfortable with the spark plugs, the next thing to try is replacing ALL of the coil boots and springs. When they are removed, after years of service, the boots can become torn and they start to "leak" spark.
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Old 07-13-2014, 03:55 PM   #6
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Originally Posted by MonsterStang View Post
At idle, the rpms fluctuate between 500-1000 rpms as well. Any ideas? Seriously feels like a loss of power
I'd get the misfire problem solved first but if the surging idle persists, you'll have to, probably, replace the Idle Air Control valve.
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Old 07-13-2014, 04:21 PM   #7
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Hmmm.

Ok. They are normally changed in sets though...

If you're comfortable with the spark plugs, the next thing to try is replacing ALL of the coil boots and springs. When they are removed, after years of service, the boots can become torn and they start to "leak" spark.

I know that they're changed in sets but being a broke college kid has drawbacks. What would a torn boot look like?
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Old 07-13-2014, 04:36 PM   #8
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I know that they're changed in sets but being a broke college kid has drawbacks. What would a torn boot look like?
I hear you. I've been there... Not college, just broke.

You probably won't be able to see it with the naked eye. It just takes a microscopic little hole for the spark to find its way through. You can just buy one boot and spring kit and do number 3. See if that helps.
Some of this stuff, you can't really skimp on Monster, it will drive you nuts chasing down problem after problem.
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Old 07-13-2014, 06:14 PM   #9
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How much would replacing the boots and springs cost roughly? And a possible place to get them from?
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Old 07-13-2014, 06:22 PM   #10
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Less than $30.
Any auto parts store should have them or be able to get them.
Or you can try Rockauto.
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Old 07-13-2014, 06:26 PM   #11
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Less than $30.

Any auto parts store should have them or be able to get them.

Or you can try Rockauto.

Alright $30 isn't that bad. Do you know anything about the air idle control valve or whatever's making my stang idle rough?
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Old 07-13-2014, 06:34 PM   #12
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And $30 is probably on the high side, they have some less expensive ones at Rockauto that will work fine.
The Idle Air Control valve is one of the things that I wouldn't cheap out on. I always use Motorcraft but I understand that the Hitachi IAC's work just as well and are about half the price.
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Old 07-13-2014, 11:05 PM   #13
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Alright. Thank you for the help and information. I'll definitely try all that out and hopefully start getting her back to full speed here soon. Thanks.
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Old 07-13-2014, 11:25 PM   #14
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No problem!
Good luck!
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Old 07-14-2014, 11:45 PM   #15
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I have the same problem, 2003 mustang misfiring, broke and a college kid haha mine tends to misfire between 30-50 mph and sometimes when idle, is there a way to trouble shoot what the problem is before spending all this money on parts that might fix the problem?


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Old 07-15-2014, 12:34 AM   #16
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I have the same problem, 2003 mustang misfiring, broke and a college kid haha mine tends to misfire between 30-50 mph and sometimes when idle, is there a way to trouble shoot what the problem is before spending all this money on parts that might fix the problem?


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Yes!
If you want to fix it piece by piece like Monster was trying to do, you'll need to try and narrow down which cylinder (or cylinders) are misfiring. Typically, there will be a code that will tell what cylinder that it is. Even if you don't have a Check Engine Light on, there still may be a code. If you have access to a scanner, that will be your first diagnostic step... Read the codes.
Or, a low tech way to check for bad coils is to buy a cheap coil and start swapping it onto each cylinder until you find the bad coil.

Basically, though, my advice is the same as is posted above.
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