Hi, i have a 2000 astra 1.7dti ls, on tickover the revs rise from 800 to 1000rpm when warm and cold, then they go back down to 800 and then up to 1000 again. It keeps doing this about every couple of seconds or so. Dont know whats wrong, can anyone help?? also the car only revs to about 3500rpm and is really sluggish until you hit 2000rpm cheers craig