I have a 2009 Cooper S with just over 72k miles on odometer. Last week, I took my car in and had carbon build-up removed. After that was performed, the car ran super rough and rattled (and even stalled on some occasions) during cold start. I did some research and figured I needed new high pressure fuel pump which would be covered under factory warranty since it's a common problem. However, I took it to dealer today and they claimed the problem was "improperly torqued spark plugs." I call B.S. Am I wrong? Will try starting car in a few hours for cold start test.

 

Easy to 2x check - re-torque the plugs to spec, and see if the problem goes away. If it does not, you were right.

I can't believe any mechanic (dealer or not) would not have re-torqued them before returning the car to you. If that's what they did, and now it runs fine, then that may very well have been the problem.

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