2007 R56, 62k miles, recently had carbon build up removed by dealer for $1000. 2 weeks later, rough starting when cold (overnight) stumbles then after 2-3 starts runs okay. Plan on putting new plugs in. Any other thoughts?

 

The infamous hpfp could be the culprit they are warrantied to 100,000 mi.Have it checked out

 

After many trips to the dealer, it was the hpfp. The fault took a while to show up.