HI

i upgraded my 1.8 escort GTI throttle body to a 2.0ltr mondeo throttle body, once fitted i took the car out for a run to see the diffrence, drove it hard for about 5mins and came to stop at sum traffic lights and when the engine was coming down from 4000rpm it cuts out, however when below 4000rpm its fine and idles perfect.

Any suggesstions to what the problem may be, faulty throttle body???