hi to all, i need some help with my golf mk3, engine code ADY 2.0l 8v, it got a missfire at 3000-4000 rpm and a slight missfire at idle, ive changed the coil pack,rotor arm,cap,leads,plugs,cat,lambda sensor,cts sensor, im getting a fault code of 00537- lambda control upper stop valve, eney help on this would be great as its doing my head in, ive also checked the timing,air leaks,fuel pressere, thanks james