Hi, I have a Calibra sports coupe that did exactly the same(apart from sometimes the engine used to race) but more commonly just cut out at low revs. Problem is your engine IDLE valve. Should be situated right next to where the air intake feeds the engine.Mine had two small bolts to take off,spray with WD 40 and bolt back.Its been fine ever since,and no cost :-) Previous owner had replaced the ECU costing hundreds for the same problem...
PHIL, October 2008