Nissan Repair: nissan micra, mass flow sensor, castrol gtx

Question
i have a nissan micar 1.0s suffering from poor fuel effiency



Optional Information:
Year: 2001
Make: Nissan
Model: micra
Engine: 1.0s

i have a nissan micra 1.0s 2001 y reg suffering from poor fuel effiency. i used to get close to 100 miles from £10 now i only get around 28 miles from £5. gosh that's bad. i've serviced the car, new oil and oil filter castrol gtx , new spark plugs ngk, new air filter new pcv filter blue print which is located under the air filter. new fuel filter blue print. i have checked the tyre pressure thats fine. i have added stp fuel addative to the petrol. the car now gives off a white cloudy smoke and is spiiting what i think is water from the exhaust. the car is not burning any oil or consuming any coolant water. the engine management light has not come on. i have removed the pollen filter due to poor heat coming through to the cabin. that's ok now since i removed the pollen filter. i have checked if any wheels are seized. There has been no drop in performance at all. the throttle body and air mass flow sensor was changed less than a year ago. please help me.


Answer
Imran,

You checked the usual suspects like tyre pressure and if any one of them is dragging.  Other causes could be the converter is melting shut and causing the engine to work harder to get the exhaust out.  I would say the converter since you say you have something coming out of the exhaust and it is not consuming oil or antifreeze.  Have the converter inspected for being clogged up or melted.  One last thing?  Timing is correct?