2009 clubman
 

i have a 2009 Clubman that stumbles when started. At first it took about 5 minutes to get it to accelerate. i put it in the shop and my mechanic changed out the MAF sensor. it did not improve. took it back and he did a walnut shell blasting of the intake valves. It was fine for 2 days and then went back to stumbling again at start up but not as bad. i went from 93 octane gas to 87 octane and it is not as bad. It don't stumble as long as it used to. It seems like that after you get it to rev up and then shut it off and restart it that it runs ok. it runs great once it gets past the stumble stage. Does and body have any thoughts on this. I have been thinking about taking it to mini dealer and have them see if it is the high pressure fuel pump. I still have a little bit of time left for their warranty to cover that. Any help would be appreciated.