I recently replaced a head gasket on my 1991 corolla with a 4afe engine. when the car is cold and I am accelerating about ready to shift gears at high rpm it briefly hesitates and then continues to accelerate. I have checked all hoses and connections. It has been properly timed to 10 degrees It has a new cap, rotor and spark plug wires, new plugs and air filter. I sprayed carb cleaner around the intake and I could not find any leaks nor did I find any leaks around the fuel injectors. I cleaned the throttle body and have checked the cold start injector and airflow sensor. all test good. could it be a water coolant temperature sensor problem? Any Ideas of what the problem could be?