Hello, has anyone any ideas please?

Our 2009 Cooper S stutters under full load in the higher gears - not at higher rev's in lower gears. Garage said it was casued by bad fuel but surely this fault would clear after several 'good' tanks. Could it be the plugs which are due for change (after 30k miles) It also has a slight misfire if you come off the power abruptly.

Any suggestions before the garage replace everything at huge expense?

Thanks.

You might try running fuel injector cleaner through a tank of gas before the shop!

Injector cleaner worked a treat - no problem at all after only 20 mile. Thanks again.

Hooray! Dealer probably would have done the same thing!