could be the blue engine coolant temperature sensor. if broken, the management (if you're name's not down, you're not coming in - sorry) will think that the engine is cold all of the time and will add more fuel (kind of like what chokes do on carb'ed motors).

to check it put a multimeter on it and check it's resistance. it should be 9.75 kOhm at 0 deg. C and 0.53kOhm at 70 deg. C. anything outside of this range and it's no good. if it's broken, you'll more than likely either have a short or an open circuit.

it's difficult to get to on the engine (inlet side of the cylinder head, at the back, near the dipstick and water outlet). you could check it at the ecu end by removing the multiplug and checking between pins 29 (black/green) and 11 (brown/green)

hth