i have a problem with my leon cupra 2001. the engine light comes on. i book it in with the dealer to sort the problem but by the time the car get in to the dealers the light has gone out. they say it shouldnt do that. when the lights on,the car runs fine but when it goes off it runs like a bag of c**p. it seems to surge at low revs for no reason and the tickover is bad. has anybody had these problems ?