Cold Starting - 1997 Move


My son has a 1997 Move which is a great car except it will not go with the starter motor from cold. However - one little push and it's away.
We have replaced all the electrics, changed the air filter and checked and cleaned the air control gear to the fuel injection but to no affect. The engine turns over well and the spark is healthy. Compression is good and the engine runs fine once going. Just passed MoT with excellent emissions result. Baffled. Is there some electronic gismo which richens the mixture for a cold start and if so - where is it? Any suggestions?