hi lee, providing all the boost pipes/vac pipes are on and good, then your idle problem could be several things, not always a simple matter of adjusting the idle air bypass screw! firstly you will have to make sure you base ignition timing is set correctly with a timing light. then it could be that the heated idle control valve on the back of the inlet manifold is either faulty or has a loose connection (it should be live with the fuel pump) common symptoms are that the car will idle fine when hot in town or slow moving traffic, but as soon as the valve cools with increased airflow at speed the idle speed can increase. This is because there is a heating element within the valve to help bring it up to temperature and keep it warm, not easy in the north east of scotland! Assuming this valve is ok, a quick Co mixture check/adjustment with a gas analyser on tickover will smooth the idle and make sure your emmesions on idle are correct, this can be adjusted then its a simple matter of fine tuning the idle with the screw on the throttle body! give me a shout if ya need a hand