I have a 2004 "justa", R50. Spent the first year with it completely trouble free. Now in the last month it's been one thing after another.

Most issues have been solved, but currently I'm getting a P0300 code and also the stability control light comes on. They don't happen at exactly the same time, but they do seem to be in sync. Some information:

The car runs great. It would seem to be some sensor problem.
I changed the fuel filter a few weeks ago.
I took the coil off and tested it. It was good.
Plugs and wires were new a year ago. (The plugs are copper, not iridium.)
I have recently done several Seafoam treatments by sucking it through the PCV. After each there was a lot of smoke, and the engine runs a little better each time.
Air filter is new.

My nearest dealer is three hours away. I hate these lights. Perhaps I should learn to ignore it, but if I want to sell the car it will affect it's value.

 

At lunch I took it to someone who has a better scanner. The P0300 code was still there, of course. But he had diagnostic information, so we went through each and every system. Everything checked out OK. Makes sense, because the car is in top shape. I cleared the code, but I expect it will come back....

 

Random multiple misfires.....
Have you checked your plugs...
Cheap copper plugs tend have a very short life....and the gap wears VERY fast...
Then make sure your fuel is good...maybe try a different station...
Then...I guess it us possible the knock sensor bad...but since you said the car runs BETTER after seafoam...it sounds like the misfires are real... So the sensor would appear to be working...

 

Also, OP, did you do the plugs yourself, or did the seller say they changed them before they sold you the car?

I just picked up an R53 a few weeks ago, so this is my mentality all the time now. "What was done here... what was done there... what do I know for sure... etc."

 

Thanks for the responses. I suppose it could be the plugs. I did them myself shortly after getting the car last July. If it is, this is the most sensitive car I've ever seen! Ok, what iridium plugs do you suggest?

 

NGK seem to work great on most MINI's.....the OEM are NGK...
to save a few $$ platinum should be fine on a non-s.
Copper plugs can have a life as short at 10,000 miles, even less with some brands depending on design.....and since the MINI uses a "waste spark" ignition (has only 2 actual coils, like most cars of this era before coils were plug mounted) the spark actually fires 2x per rotation.....

One tip...
on the r50 the suggested temp plug changed over the course of the cars life...so you might want to check more than one listing for the right plug....or just buy them from a vendor that will get you the right part..
if I recall the change was due to MINI/BMW in car experience as opposed or just published in error...

and one reminder....
you must use mid-grade (actually one point too low in most areas) or higher for fuel...the high compression motor can be damaged,,usually the Valves get burnt overtime from using 87...this usually manifests itself as a misfire on ONE cylinder that rapidly worsens...what happens is the valves get too hot from not enough octane...and they get "burnt" and then they are soft...and rapidly wear or even fail....
many debates have occurred over the years....but the general result is you can save 1$ per fill up, but it might cost you a $1500 head job.....

 

Ok, i just now put NGK platinums in there, and wow, the car runs like a banshee. Better than any time that I have owned it. Now I hope the light stays off. We shall see.