Man....so here's the scoop: When my engine is cold, it starts fine. When it's really hot, it starts fine too. But anywhere in between and it has to be started more than twice before it finally kicks. And sometimes, when it finally does, it rumbles as though one cylinder was misfiring.

I checked the timing but I'm beginning to suspect the ISV. Thing is I don't have a Bentley manual. So how do I open the ISV to clean it?

Thanks in advance, folks!

behaps.... injectors?
those things do crazy stuff to a car too :)
I don't know much about ISV, sorry

Is it Turbo? ISV is located on vacum hoses to the rear top of valve cover and connected to crankcase vent and air intake by 3/8 ID hoses. Disconnect wire connector and then disconnect hoses. Spray exposed little disc end with wd 40 or similar and use a tooth pick to clean it. No metal points in there or you may damage it. Disc should move freely after cleaning. Also could be a problem with temp control/sender located at bottom of thermo stat housing. The contacts get corroded and all the connected sensors (ISV)get messed up. Bimmerparts.com has/had replacement parts. This is a good reasonable parts source.