quick question, if a s2 erst metering head was fucked would it play up all the time or just when starting the car

The car takes a good 30 - 40 seconds of cranking before it splutters into life, once started it drives fine with no missfires but I have noticed a low idle and lots of 'rumbling' when you lift off the throttle.

Or does this sound more like a problem with the fuel ecu ?

cheers, Duncan