check dizzy cap if moisture is in there, same for cables
check engine temp sensor using an ohm meter (multimeter - 10£ one from b&q/homebase/halfords will do):

it's a dual sender, one goes to your instruments the other to ECU... if it's broken the engine would use a standard value, in cold weather that could cause too little petrol being injected...
if you got a diode test lamp or an oscilloscope (or a cheapish ebay DSO) check if the crank sensor is working when you crank the engine, although this would normally also give you trouble when it's warm.