The Mini has a persistent miss, cylinders 2 and 4, codes P00302 and P00304. Started on the freeway on a long trip. Changed the plugs and coils, still there. Any advice? '07 R56 Cooper S, 98K miles.

 

There are a few diagnosis for P0302 and P0304. Some good readers will be able to tell you the MINI FC associated with the P code. Some info on P0302 here and P0304 here. Just a thought, ever done a carbon clean up on your R56? Just about every 50,000 miles the intake valves need to be cleaned to maintain optimum engine performance. Once the build-up reaches the maximum tolerable level, the engine will begin to run rough and misfire. You may have a rough idle, poor acceleration, stalling or single to multiple cylinder misfires. If you have any of these symptoms, check for valve residue build-up.

 

Try to clean up the possible carbon on the valves.
Seafoam should be an option (I have a bottle and I will do it next week, without having any misfire issue).
There is a lot of videos "seafoaming" a Mini.

Let us know!

 

Yep, if you haven't had the intake walnut blasted, you're past due..