Toyota Celica automatic choke not working straight away at start-up, drinking petrol and jumps at low speed

Hi there, im having a bita trouble with my celica.. at start up the choke doesnt seem to come in unless i hold the revs at 2000rpm for a few seconds and even then when it does come in when u rev it the revs dip right down and the car just bogs then itll pick back up... also if you drive slow in 3rd gear the car jerks which neither of these happend before.. the car was standing on my driveway for a month untill last week up untill then it was running perfect. i've changed the plugs and replaced air filter. i've been told it could be the temperature sensor but thought id ask you guys first as parts for this car cost an absolute fortune :/

any help would be appriciated

thanks

Lee.