I have a weird issue I could use some advice on. I have a 2011 Cooper s, with some mods and tuning. Mileage is at almost 95k. I was driving down the highway, went to pass someone, and heard a loud pop and felt a pretty major misfire, along with a check engine light and reduced power warning. Pulled over and shut off the car. I didn't see anything obviously wrong I didn't already know about. Decided to start it up, and the reduced power light came back, but went away after I started moving again. The check engine light was still there though. I otherwise got home without incident, outside of the turbo doing little to nothing, but that might have been because I was driving like a grandma in that last mile or two home. I borrowed my mom's Camry to get to college classes today, so my mini hasn't driven since coming home from the incident.
In case this helps, I have had a minor leak from the top passenger side corner of my valve cover that started a little over a week ago. I also notice the engine idles a little rough when first starting, even when already warmed up.

Mods done:
- M7 tuning CAI and intake boot- Milltek 2.5" catless DP- Invidia Q300 DP back exhaust system- CTS Turbo FMIC- Colder stage NGK plugs- Dinan ignition coils- stage 2 tuned to 93 by lou

Maintenance/repairs done recently:
- valve cover replaced by me a month ago- plugs and coils 3 months ago- clutch replaced 6 months ago- HPFP replaced almost a year ago

​​​Any help/advice would be apriciated. Thanks for taking the time to read this literary abomination.

 

Forgot to mention, codes that came up when I scanned it were P0300, P0302, and P0303.

 

@Deceptic

Check the large hose that goes to the intercooler located on the right side passenger rear of the engine compartment like the photo below. Mine popped off and threw a bunch of codes.

 

Do you have the freeze frame data from the misfire event? If yes, what was the engine temp (ECT) at the time of the misfire?