Nice car...I didn't know they made the turbo after 93...two more years to look for a replacement for my 90 740T.

Anyway, if the service bulletin doesn't help, you can also check the intake valves for deposits...sometimes the BG44K won't take off the intake valve deposits (IMHO it's best for fuel system/fuel injectors rather than combustion chamber or IV deposits).

An engine with significant intake valve deposits will behave exactly as you note, runs crappy until the intake valve and deposits get hot enough to quickly vaporize the fuel that gets sprayed on them during the intake stroke.

There are machines that remove the intake valve deposits without pulling the head...have to take off the intake manifold to access the ports and then the machine is bolted up and blasts the intake valves/ports with crushed walnut shells and vacuums the shells out. A few shells left in won't hurt the engine when started and shot out at idle, even with a turbo.