I posted here a few weeks ago about this issue. Car is 2002 Passat, around 120k. Cylinder 5 misfires heavily at cold start, runs fine when warm. Done so far: new ignition coil, cables, spark plugs, dealer checked compression-good on all cylinders and "flushed" fuel delivery system(that made it misfire on 2 addition cylinders). Dealer said ecm was bad so I had it rebuilt by BBA twice (after first rebuild didn't change anything). BBA supposedly tested the ecm and confirmed it was bad, I say they are full of sh.. and just wanted to collect my $500+. Now I am back to misfire in #5. Spoke to a local VW specialist who is suspecting carbon build up. When I pulled the old plugs out they did have heavy black deposit/crust on them, maybe worse on cyl 5. What's the procedure to clean the carbon buildup on these engines?