i own a toyota celica ST164 89 model the problem is when i push the clutch in or in neutral its revs go between 2000 - 3000 RPM but when i first start it after about 15 mins resting it will stay at 1000 RPM after i drive for a while it will go up when i push the clutch in for a while first it will go to 1000RPM what could it be??????