Sometimes, on cold starts only, the RPMs will oscillate a bit as if the throttle is being blipped on my N55. Can go above 1000rpm while 'blipping'. No check engine or warning lights, but I've felt/detected a misfire on some of these cold starts. I think this is normal since others with N55's have reported similar behavior, and that this is BMW's way of dealing with some of the challenges that cold starts with direct injection presents. Audis have had similar issues, I think. On the Lexus 'dual injection' engines that have both port and direct injection (2GR-FSE, 3.5L DOHC, 306hp IS350, GS350, etc), they actually run 100% port injection on cold starts to get around this. It also fixes the intake port deposit issues that pure DI engines have. I think the blipping allows it to run a slightly higher idle load which gets around the issue. When it does this, which is not all the time, it purrs like a kitten with a nice smooth idle after 10-15 seconds.
Last edited by SteVTEC; 01-19-2012 at 06:13 PM.