I have tried to clean a MAF several times. It has worked sometimes, doesn't feel like it is back to 100% and doesn't last long. At least by cleaning it there was a noticeable difference that was indication it was sick. When you clean a MAF spray the inside wires for an extended period of time and at several angles. Those are the important wires. There is a throttle body cleaner or you can use carburator cleaner. Clean it will the engine off and it may be difficult to start after. You will need to remove the air intake tube. Before you clean it, with the engine running, watch the throttle body and see if it is moving while at idle. If the problem is a coil it is best to change all 8 as many times the other start failing, some say because of the new one, not convinced that is why. I would look at the spark plug in that cylinder to see if it light brown, even if it is I would replace it. There is little you can do to test a coil. You can attach and ohm meter to the two outside terminals and it should read between .4 and .8 ohms. The easiest way is to swap coils and see it the the INPA shows the problem has moved. If it hasn't it is not the coil.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas