Hello!

So 2010 S Clubman started shaking and rough start/idle. Giving me random misfire and cylinder 4 misfires.
Here is what I've done:
Checked for leaks - none
Checked valve cover for cracks - none
Removed valve cover to replace gasket - no improvement
unplugged the electrical connector from each coil one at a time- when removing 1-3 the engine slows or almost shuts off, unplug 4 and nothing happens.
Swapped coils - same issue but still only on cylinder 4
Removed spark plugs - all looked good except cylinder 4 plug was black and covered in soot. (could not see anything wet or oily at the base of the plugs)
Replaced spark plug with new one - nothing
Checked that the 4th cylinder connector was sending power to the plug - check, it sparks!

So what is left now? Check the injector? Obviously things are working down to the spark plug but after that something is going awry.

 

as you said, you could check the injector. If you just remove plug 4 and start the car, there should be puffs of gas coming out. if there is gas puffs, you need to do a compression test.

 

 

every now and then, the exhaust valve burns or chips away. The repairs for this at a shop will cost a pretty penny. if you DIY, you can save a whole lot. Where are you located btw?

 

 

Yep, bet it's a chipped exhaust valve. Have a leak down test done to know for sure. Somewhat common on these cars..