I was having similar issues with my v36. Was getting about 300-325km per tank.
Annoyed me enough to do the following
Cleaned MAF Sensors, Replaced filters, Reset ECU
unsure if the ECU on the v35 is "self learning" like mine but when you reconnect it all, Drive in (D) only for about 50km (drive like a f**king grandma, slow and steady)
I did this and now i get atleast 500 to a tank. i got 700 on the highway before i filled up.
Also as fun as it might be to drive in Tiptronic, it will make your economy worse. I only use it every now and again.