My 07 Mini is brand new to me, but has 80,000 miles on it already. I bought the car from a certified Mini dealership (who filled it with 91 octane gas) and didn't experience any problems for the first few weeks I owned it. I drove it from Philly to Texas last week and on the third day of the drive it began to shudder when accelerating uphill. Yesterday the shuddering was more pronounced when simply accelerating or when idling at stoplights, but then the problem disappeared completely for a while on the way home. I'm not much of a car tech, so I was hoping more experienced Mini owners could advise me on the seriousness of this? It never feels like the car is less responsive when it happens, more like it's just clearing its throat. The computer hasn't registered any error indicators and there are no warning lamps lit. It's not due for a service check for another 6000 miles.
On the first day of the long roadtrip, I experimented with filling the tank with 89 octane. Could the shudder be related to the "knocking" that the owners manual reports could result from using fuel below the recommended 91 octane? Since the problem started I refilled the tank with 91, but the tank wasn't completely empty when I refueled, so logic dictates that there is still a mix of gas in the tank.
Any thoughts would be welcomed and greatly appreciated.

 

You don't say if it's a regular or an S the S are more prone to knocking with lower quality fuels. I cannot run several brands of gas without experiencing knocking...
It could be a miss , bad plug or wire