I took it to a BMW dealership. They ruled out the coils, injectors, plugs, catalytic converter. It basically falls down to either a burnt/faulty exhaust valve or carbon build up. I don't have the skills to replace an exhaust valve and the cleaning at the dealership runs a little over $700, but I figured I could try out Seafoam.

Thing is, I read something about how a piece of the an exhaust valve broke off and busted up the engine after a Seafoam cleaning.

Is something that I should worry about? I don't have a lot of money, so I try to do a lot of stuff at home. Is it a real concern?

 

What year car?
Since you posted in the gen1 area...making it a r50/52/53 (2002-2006 hardtop, 2008 cabrio)....I would suggest a "carbon cleaning" is likely not worth the $$...gen2 car...maybe IF it is an S....
I would wonder WHY a compression check was not done as a first step...THEN a leak down test...as easy as changing the plugs....this would confirm it is mechanical, and point towards or eliminate the valves, or be OK. Pointing you towards a electrical issue....
You might want to get a shop that knows something about cars IMO.

 

After your leakdown test and compression test you'll probably discover that it's a burnt valve. Pulling the head and having it rebuilt really isn't that hard. If you're even half of a shade tree mechanic and have a good tool set you'll probably be able to do it.

A torque wrench, new gaskets and the $75 ebay camshaft gear removal tool will be your best friends on this.

Good luck!

Val

 

A burned valve will easily show with a compression test and leakdown test. Either is easily done by yourself with simple tools. Check Harbor Freight for both if you are cheap.

If it is a valve, you're looking at a steep repair bill at the dealer on top of the $700 test, which is ridiculous IMHO. But taking the head off a Mini engine is a lot easier than you might think. A metric socket set and a torque wrench are about all you need.

Take the head off and have a local auto machine shop fix the valves - as long as it's off, get them all done. If one is burned the others will not be far behind.

The procedure, including replacing valves is in the Shop Manual, get one if you don't already have one.

But I'd try Seafoam or Techron fuel injector cleaner (my favorite) as the issue may be a clogged injector. I don't think either is going to cause bits to fall off your valve. The valves don't know either is in the fuel, it's just extra detergent.

 

You should be able to find an independent shop to do the walnut blasting (carbon cleaning) for less than $400 if that turns out to be the problem.