my vw golf mk 2 16V 1990 runs rough at cold?

can anyone suggest what the problem might be, basically when starting from cold it runs roughs, strong smell of fuel. it could be the cold start valve, or maybe a sensor that controls it? once warm runs fine. have checked cold start value and it does have an even spray pattern and doesn't drip.the problem does not occur everytime, that's why i think it might not be the valve itself, but rather a some sort of sensor?
many thanks for any suggestions.