I drive an 2011 MCS with 39k miles on it. It starts fine, idles fine and runs smoothly throughout the RPM range. But when I engage the throttle wide open, I get hesitation and a half CEL. I scanned for codes and found one: P0302 Cylinder 2 Misfire.

Fluid levels are OK. I change oil every 7500 miles, and spark plugs and coils are within replacement interval. Air filter was changed at the dealership at 30k miles.

What's could be causing this problem?

 

Replace those crappy beru spark plugs. The factory installed the wrong heat range plug.

 

Try swapping the coil with another cylinder and see if the code changes..

 

Thanks for the suggestions so far.

I will try swapping coils and report back.

About the the spark plugs. If they are "wrong," how come it never misfired before? What is the right heat range plug? I've seen Laser Iridiums mentioned around here. Should I get those?

 

I doubt the coils would be failing at 40k, spark plugs yes, remove the plugs and check them for damage, the porcelain around the electrode on BERU's have been know to break/become loose. The NGK laser iridium plugs are an upgrade.

 

should get the codes scanned by a proper tool. The half engine lights will log faults that most generic scan tools cannot read. The misfire code might be a result of something else you are not seeing.

 

OP edited.

 

Plugs or coils.

You could try moving the coil from cyl 2 to diff location. If you end up with a multiple misfire code afterwards then bad coil.

 

Um, I'm not sure what I did, but the problem went away.

As suggested, I swapped coils #2 and #3. I checked the wells and saw that they're free of oil. I didn't have a 14 mm 12-point deep socket, so I could't inspect the spark plugs. I put it all back together, making sure that everything is snug. Upon starting I noticed that the engine sounded and felt different. Better. I drove her to an open road and floored it! No stumbling, no misfires, no codes.

The tires chirped though

Thanks anyway fellas!