corsa b 1.6 16 valve engine problem

[stuartA879]

when i start the car first thing ,it runs and starts first time but when it heats up you have got to try and get the revs up past 2000 revs before the car will pull away and it also back fires inside the air filter,but when you drive it out on the open road you would think ther w as nothing wrong at all.i have had the car at 3 different garagesand it has baffeld every one,but it is a replacement engine of the same kind.all sensors have been replaced.does this sound like a fuel problem.thanks.stuart

[heretohelp]

has it been plugged into a diagnostic computer if not try that first,if there isn't any trouble codes try replacing the coolant temerature sensor first,it could be the coil pack or plugs aswell.