coil packs
 

1999 mustang gt- bought it back in july, always felt a little bit of miss when idled but nothin bad, if this were any car that actually had spark plug wires i would have thought one of the wires was going bad. I recently bought a set of spark plugs for the car (thought id start their) well i ended up not replacing them because after pulling the first one i realized that the previous owner must have put new plugs in within the last 10k miles or so because they were almost new looking bosch platinum plugs. Im going to guess i might have a COP thats not working "perfect" but still working . ive heard about ppl just replacing one or 2 cop's but how do you figure out which one is bad? from my perspective i see almost no way, it seems like its a trial an error type thing (keep replacing them one at a time till you fix the problem)

run the codes, see which cyl throws the missfire code.

Its not real common for a COP to go bad, but find out which cylinder is misfiring and then swap the coils and see if the miss moves with the coil.

well the car throws no codes or anything so its obviously not that bad (i can notice it at idle but thats it, i doubt anyone else would even notice it)...like i said i dont know that it is a cop or not its just the next thing i thought of..im probably gonna take a look at a few other things this weekend..ive got some ideas of other stuff that it could be.

start by running the recomended spark plug first.. We see alot of this type of situation in our shop, people coming in complaning thier car is not running right.. first thing we check are the plugs, 80% of the time they don't run the recomended plugs, a quick change to the right plugs fixes the problem..some people like to play engineers and think they can put a better spark plugs than the ones recomended on thier nearly stock car..

Agree with stang5. I have personally however seen tons of ford COP vehicles have bad COP's.