I have this same problem. When I start the car, it rumbles a bit and you can feel it through the shifter, etc. I just had my spark plugs done maybe a month ago, and do not remember it doing this before. I have had the procede out since my spark plug job, and also have the exhaust plug disconnected. I dont think its misfiring as no check engine light comes on. It's just a little rough at idle. Today, I went to the stores, and came home car is warmed up, and idled it in the garage. After a moment, it stumbled at 600rpm, then rose to 700rpm and stayed there. I shut it off after a minute like that...no stumbles at 700rpm. I wonder what the problem is.
2007 BMW 335i, Jet Black, Sport, 19" Wheels, custom trim, m shifter, Procede v5 Rev.3
369rwhp, Best 1/4 12.8 @ 108
2003 Hyundai Tiburon GT, Supercharged (stage 2, 280whp), Full mods, meth, coilovers, wheels, full stereo
2004 Suzuki GSX-R600, flush signals, undertail delete, carbon fiber exhaust