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Discussion Starter #1
My 2002 mustang GT, 105k miles, has been kicking back and forth when idling or at cruising speeds. It happens spontaneously and its not very drastic either.

It all started about 4 days ago when I did a couple of hard accelerations (4000rpm). I have had this car for about 4 months and very rarely floored it or never raced it nor any crazy stuff.

I have spent hours and days researching online and nothing. So I decided to join an online forum to shed some light.


When this happens the rpm's seem to stay constant. It just stumbles/jerks/kicks when accelerating.

My inexperienced college student diagnosis:

-I don't think its the transmission (no slippage, grinding, nor weird revving when changing gears)

-Its not a dirty IAC because it happens at cruising speeds as well as idling

-I'm thinking I blew something since it happened immediately after the hard accelerations.

I am not at all an expert, but Im thinking:
-blew a spark plug?
-O2 sensor?
-A hose of some sort?
-messed up U-joint?
-fuel injectors?

Not sure if this could have anything to do with it, but I recently lowered my car about two weeks ago. It dropped more than expected (2.5 inches all around) and I have hitting underneath my car on bumps and crappy roads.

Thanks for reading. Any advice will be appreciate it.
 

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My first guess would be spark plugs.

Doubt you blew one out, otherwise it would miss all the time. And you would have heard a pretty good bang or pop when it happened.

Check Engine light on or flashing?
 

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Sounds like a Mis-fire...Could be a bad Coil On Plug or plugs, or spark plugs as memtioned above.

Our PCMs tend to not report codes with misfires but that's what it sounds like to me.

Is the CEL on? Do you access to an OBD2 scanner that can display live data?
 

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Discussion Starter #4
Thanks for the replies guys.

The check engine light is not on and I do not own a scanner. Spark plugs is my main guess too. I will be changing them tomorrow. I heard to stick with oem plugs correct?
 

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I prefer Autolite 764's which are a copper plug. You can get all 8 for about $12.

Otherwise yeah just stay with a regular platinum plug like Autolite AP764 or equivalent. Gap at .052", use anti-seize on the threads and torque to 11-14 lb/ft and not a hair over.

Copper technically offers less resistance to current flow and so theoretically would be a better spark than other metals. Theoretically. On a car without a power adder it really doesn't matter; the main difference between copper and platinum is service life. Coppers will last 30K or so, and platinum will go about 50K or more.
 

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Discussion Starter #6
Changed the spark plugs and helped a lot, but it was still there. It went away on its own couple days later.

Now, Its doing it again. It was also after a couple of hard accelerations.

Im also hearing a whistling sound when accelearating and this time, the service engine soon light came on. I recently degreased my engine too if that has anything to do with it

Thanks for your time.
 

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Whistling sound?

Check anything and everything vacuum related. Chances are something was overlooked when you put everything back together or maybe came loose. If you can get the code(s) read, do so and post back.
 

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Discussion Starter #8
Problem solved!

So I took to advance auto parts and o'reillys, both said there was a misfire on cylinder 5. I decided to just buy the coil boot first for $6. Replaced it, but problem was still there.

I watched a youtube video showing you how to test for a bad ignition coil. So I unplugged cylinder 5 coil and the car's power decreased significantly, so I thought that definately was something else.

I was about to give up and just take it to a mechanic, but the manager at advanced auto parts was really helpful and told me to go head and just buy it anyways ($50 but he took it down to $30) and boom! Fixed.

So I guess that eventhough the old ignition coil was not completely out, it was half-assing and performing poorly.

My GT runs like new. Thanks guys for the time.
 

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Glad you got it back to glory.

For future reference, testing the coils' primary and secondary windings with a multimeter (checking resistance) is really only helpful or conclusive if the coil is basically cooked (open, little or no continuity). As you just experienced, the ohm readings can come back as textbook perfect but still be a weak coil.

The only way to really properly test them that I'm aware of involves use of an oscilloscope (which unless you're an electronics engineer would not be a readily available piece of equipment nor would the average person know how to use) or load testing equipment such as a competent auto shop would have on hand.
 

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I had an intermitent mis-fire and I bought come Ebay coils ($50 for 8...china crap...) and it fixed it. Been runnnig these for about 10k miles and no issues. Our computers, I'm finding, are terrible at reporting mis-fires, especially slight, intermittent mis-fires...glad you got it fixed!
 

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I had an intermitent mis-fire and I bought come Ebay coils ($50 for 8...china crap...) and it fixed it. Been runnnig these for about 10k miles and no issues. Our computers, I'm finding, are terrible at reporting mis-fires, especially slight, intermittent mis-fires...glad you got it fixed!
I had the same issue with a "slight, intermittent" misfire Jon. And yeah, no cel.

+1 on Ebay coils. I was strapped at the time and pulling my hair out for a solution and got a set from there. They were at my doorstep for about $80 and been on for about 3 years now, problem free.
 

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I had the same issue with a "slight, intermittent" misfire Jon. And yeah, no cel.

+1 on Ebay coils. I was strapped at the time and pulling my hair out for a solution and got a set from there. They were at my doorstep for about $80 and been on for about 3 years now, problem free.
This is why I bought them. I knew you and some others had good luck with them so I figured for $50 why not...best $50 I have spent in awhile...
 
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