Code P0303 (Ignition systems) & Code C1201/51 (Engine control system)
 

My 2011 xD threw the following codes this AM at ~133,233 miles:

Code P0303 (ignition systems)
Code C1201/51 (engine control system)

The symptom -- minor surging when under load, as well as when stopped) -- began yesterday.

Plugs and coils were replaced at 124,688 and the vehicle has been running nominally until now.

Code P0303 points to ignition coils, spark plugs and intake manifold gasket. I believe that cylinder 3 is potentially the culprit. (Is that the 2nd coil on the left or right when facing the engine bay?)

Code C1201/51 refers to an engine control system malfunction signal which continues for 1 second or more.

Please let me know if you can shed any additional code definitions and/or any ideas regarding where to start troubleshooting after the #3 coil is checked?

Cheers!

Most engines number the cylinders from the driver side and front to back.

Thanks for the feedback!

I'm going to switch the coil from cylinder #3 with #4 and see if the code changes.

If that does not occur, I will switch the plug from cylinder #3 with #1 and see if the code changes.

If that does not occur, perhaps the suspect is a stuck fuel injector in #3...

More shall be revealed later today...

OK, if you had accidentally mis-attached coils, your engine would've been running like a washing machine with a bowling ball in it. A mis-wired 4 cylinder is NOT subtle; Harley Davidsons idle smoother! If a coil had been mis-attached, your motor would make loud backfires, and would idle rough enough to be heard from 1000' away. Your recurring rough idle is much less severe.

To complete the loop:

The practically new (Denso Iridium) plug with ~7,500 miles that was in cylinder #3 was bad.

To troubleshoot I moved it to cylinder #2 and sure enough code P0302 was recorded. I purchased a Bosch Iridium plug at O'Reilly's and installed it and all is well...fingers crossed...

Thanks for the feedback. I'll keep this in mind if something transpires again...