I had a similar problem with a car at the workshop a month or so ago. Have you checked the sparkplugs for sparking indevidually? Presumably your a mechanic (having Autodata on your laptop..) so you may have the right diagnostic equipment.. Other than that, the reason for the car that we had in was overfueling. Being that that was a Suzuki Grand Vitara... it was a real arse to work on. We checked everything and found to be overfueling, after cleaning the intake system we found the fuel sensor had got a bit gungey and was sensing too much air, thus pushed more fuel in. Il see if there is anything about the net, I have never really needed a wiring diagram but would be useful to have.