[preppyr6]

Hey everyone,

I'm new to the N55 (picked up my 13 E71 a couple months ago with 90k miles), but not new to BMWs. I do most of my own work as I'm pretty comfortable around BMW engines.

That said, I'm nearly at a loss with my current problem.

Patient: 2013 E71 X6 N55. Only mods are Burger Air filter and M-sport exhaust.

Symptoms: After walnut blasting to get back some of the pep in the motor, I've had a subtle but notable rough idle. Its less noticeable cold, and very noticeable warm. I get no codes thrown and above 600rpm the engine feels just fine. This was my first diy walnut blast and I was careful to make sure the valves were closed for each set I cleaned. Intake manifold gaskets were replaced before reassembly, MAF was cleaned, and throttle body was cleaned.

After reassembly, I noticed the rough idle. I rechecked my work and found no issues. At this time, I had no fault codes.

Since then I've tried to track down every possible culprit. Not in order, Ive done the following:

Replaced PCV/Valve cover
Replaced coils
Replaced spark plugs
Pulled and cleaned fuel injectors (replaced teflon seals and decoupling rings)
Ran techron (I know it serves little purpose in a direct injection motor)
Ran smoke test for vacuum leaks (found one, but it made no difference to rough idle)
Reset idle adaptation in INPA (I think...since its in German)

Ive triple checked all the vacuum connections.

Running INPA rough running test, I can see that cylinder 6 is running poorly, often way out to the edge of range (in the red). I pulled the plug and its fairly black (but not completely fouled).

My next guess is a possibly leaking fuel injector BUT I dont understand how this could be a result of the walnut blasting.
IF thats not the case, then my culprit would have to be either a manifold crack (which I would expect would show up in the smoke test) or a problem with the wiring to the injector or coil (fuel issue or weak spark)...but I would expect those would give me an error code if that were the case.

Its getting cold here in DC and I dont have a garage, I ordered a replacement injector to test that theory given what I can see in INPA, but beyond that I'll need to take this into a shop as I dont have experience running compression checks on motors this sophisticated.

FWIW I ran a borescope down the plug holes and could see some carbon buildup on the pistons.

Any other ideas about what could be happening? Is it possible I damaged an intake valve during blasting or an exhaust valve was burned from poor combustion afterwards? It seems so unlikely, but this has me fairly stumped.

Ill post up vid from INPA rough running when I have a chance as well as borescope pics from Cyl 6.