Im an owner of a 2003 Ford Mustang 2-door 3.6L.
Since I got it, it have been running extremely rough when idle and while accellerating. The whole car is shaking.

I have had the sparkplug cleaned, fuelinjectors cleaned, fuelfilter changed, sparkplugwires changed, cleaned throttle body and mass flor meter, changed camsensor and synchronizer.

Nothing have changed, and my car is still running rough as before.

Just recently, the checkengine light came on, and indicates that sylinder nr. 3 is misfiring. Advance Auto Parts, told me that this indicates that the ignitioncoil is the problem... Someone who had the same problem?

 

Sounds about right, also you have a 3.8l

 

Yeah I'd say ignition coil too. Be sure that you get one from motorcraft and not some humbug brand.

 

The man is correct. OEM!

 

MSD.....

 

Is this a humbugbrand?

http://shop.advanceautoparts.com/web...=ignition+coil



And is ignitioncoil something I can switch myself easy? Or should I consult professional help?

 

Yes, make sure it's either motorcraft or msd brand, motorcraft is factory original brand, msd being performance, I've heard bad things about screamin demon, but no actual experience with that brand, I have msd and love it.

 

Disconnect battery -unplug the old one - unscrew the 4 screws that hold it in place - take old one off - put new one on - put the 4 screws back in - reconnect everything - reconnect battery - DONE!

-> Not to sound like captain obvious or anything; but be sure to put the sparkplug wires back in the right place in the right order. <-

 

What I did was left all the plug wires connected to the coil, unbolted the coil and bolted the new one on then swapped the plug wires over so I made sure they were all back right

 

Did that fix it?

You might want to treat yourself to a new set of plug wires to finish the job. As recommended above, don't get the cheapest one you can find.