E30 Zone

just got 325 tourer. pops farts and miss fires really bad. seems to clear when you turn left or exit a roundabout for a couple of seconds. does not idle as soon as the temp gets above the blue and miss fires even worse. any one got any ideas before i spend money in the wrong place. i have been told that it could be the idle control valve

if it seems to clear up when turning a corner of any sort it could well be something to do with the fuel pressure or delivery. it isnt by any chance an after market pump that has a few inches less depth than the standard item therefore not picking up when the car is under 1/4 full
is it any better when the tank is full?