Chevrolet Matiz throttle body?

The engine is holding the revs up (1500-2000) before settling to tick over quietly after about 15seconds. The revs increase a lot between gear changes going up but not usually when coming down. Using a lot of fuel. Seems like an air leak but checked everything. The throttle body can be heard clicking erratically with the rev changes as if it is getting random signals from somewhere. Car is fine when cruising along, starts Ok etc. Any help would be very much appreciated. I posted something earlier but messed it up a bit but this is a better description. Done 45K, service, timing belt done etc etc