This is my first post so please excuse any blunders in formatting or etiquette.
I have a fairly modified, low mileage 2007 MCS R52 which has an intermittent P0300 issue at idle. I have tried to resolve the P0300 by every means; Mini dealers do not want to touch the car since it is not stock or other shops do not want to work on it either because it is not using their cam/tuning package etc. I have been on my own with this issue using a process of elimination; I am at the point where a decision needs to be made since I can no longer drive it.
Background: Issue first appeared hours after the first RWM tune with new 550cc injectors. Tracked it all day with no issues until I parked and it cooled down, got a P0300 upon cold start up. Configuration at that time was JCW CAI, Stock CAM, Stock IC, 15% pulley, RMW tune, 550cc Dekka injectors. The code was fairly infrequent in the beginning, disappearing for months at a time until now where it occurs within 40miles of use. Still occurs during initial startup, you can sometime hear the misfire and stumble. The DSC light may or may not occur at the same time.
I have replaced most everything else; new ignition system twice, PCV, MAP and TMAP sensor, New 550cc injectors, IC boots, injector cleaner, tested compression, looked for HCs in coolant, tested for intake leaks, etc. The item that I have not changed yet are the fuel filter, fuel pump (doesn’t feel like fuel starvation), crankshaft sensor, or cam sensor.
It is very intermittent so much that I can't smog it thus no registration renewal for me.
The questions I have are:
1. Could this be a tuning issue? Tied to engine temp, air temp, etc
2. If not the result of tuning then should I return to a stock tune and injectors, use the dealer to troubleshoot it, pass smog, restore performance using remote tuning from Bytetronik.

 

checked plugs?

 

I think you answered your own question: If the trouble started the day after you got a tune and what sounds to also be newer injectors, reverting to the stock injectors and stock ECU tune will likely tell you if the recent work is the source of the issue. And frankly, it'd be a bit obtuse to overlook the fact that the issues are likely related to the recent work. When you have recent work done, and a problem occurs almost immediately after said work, it's always best to back-track to before you did those modifications or changes. Forgive the comparison but, think of it as using the "restore to previous" function of a Windows computer.

P0300 is a random, multiple cylinder misfire code, and will generally have more to do with fueling than it will ignition. The ignition systems on these cars generally throw isolated misfire codes, pertaining to only one cylinder. It's also doubtful it's the plugs so long as you're running the right gap and heat range.

Additionally, are you sure your injectors are Dekas ? The 550s that RMW sells now are Bosch units (Bosch# 0280158117), and proven to be suitable for this motor. Earlier offerings by RMW in larger injector sizes were incorrect for this motor, as documented on MiniTorque by several people (flow & pattern tests were performed).

You just modified your fuel system and associated tune; what do you think the problem is? Keep it simple. Install the stock injectors, get back to the stock tune, disconnect battery & let sit for a few minutes. Reconnect battery, and drive the car in varying conditions for a few days. Get back to us.

 

Since multiple misfires started RIGHT AFTER THE TUNE....thinking you have an issue with the tune or the injectors you installed right before you tuned...
You are still using the same octane fuel you tuned on right?