what could be wrong

[speedophile]

i have uk twin turbo supra that has been parked up due to a faulty alarm this past month, the alarm has been took out but went to start the car for the first time and the car seems to be under fueling and the rev hand is dropping to 500 and less in revs i left the car running for 20mins but its still spluttering like its going to cut out... then i took the car for a short run down the road but from leaving the house to getting back there is wicked steam leaving the exhaust covering the road behind the car.. its steam and not smoke as i got the wife out to rev the car at the front of the house and its just crazy the area it covers when reved but when you lift your foot of pedal it goes back to spluttering... the car is well looked after and all coolant level and oil levels are good

any ideas?