a vanos problem is the variable valve timeing unit and yes its a big and very expencive problem on evo m3s (3.2 ones) the older 3L ones have a rolls royce unit and dont have the problem. If its fucked it should rattle stop on your test drive open the bonnet rev it to 2000rpm then let it drop to idle and see if it rattles its the silver lump on the front of the rocker cover! It should pull hard in second gear in the midrange then feel like a sort of power band till the red line but they can go without any warning!