92blackbandit

I recently purchesed a 92 z28 with a 305 tpi. The car only has 63000 miles on it. The only mods it has so far are hypertech chip, 160 theromostat and air foil, flowmaster catback exhaust, k&n air filters, 4.10 richmond gears, and shift kit. The car has been givin a tune up. The car runs really strong but the only problem is when the temp is below 40 degrees F when i first start the car the rpms jump between 500 and a 1000 for like 5 minutes then it's fine, but when it's above 40 degrees it dosen't do this. Is this normal?