[jpmb]

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?

 

[90 GP]

Check your computer for stored codes. Sometimes they are stored but don't trip check engine light. Here is link on how to do it. If no codes check for vac leaks and check out throttle position sensor and EGR valve and associaciated plumbing if your car has it.

http://www.troublecodes.net/Toyota/

 

[Flashmn]

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.

You shouldnt race a cold engine anyways...

 

[ELUSIV Rolla]

you shouldnt race a cold engine anyways...

agreed!!

 

[jpmb]

thanks for the link. I checked for codes. Everything is functioning properly. Any other ideas?

 

[Donald]

Have you replaced the injector "O" rings and rubber bushings?
Those should fit tight. That is a prime place for air induction when those get old and harden.

Is your idle speed correct when cold and when hot? If not your idle air control valve could be sticking.

 

[jpmb]

Yes I did replace the o rings and upper bushings and lower ones that are refered to as insulators. that did not help. the idle speed is correct. i have sprayed carb cleaner aroud the engine to check for air/fuel leaks and the engine does not respond to it. So I am guessing there are no vacuum leaks.

 

[Donald]

Yes I did replace the o rings and upper bushings and lower ones that are refered to as insulators. that did not help. the idle speed is correct. i have sprayed carb cleaner aroud the engine to check for air/fuel leaks and the engine does not respond to it. So I am guessing there are no vacuum leaks.

Seems like you have most of the basses covered. Time to tackle the idle air control valve.

 

[90 GP]

To clean the IAC remove the rubber air intake that goes from air filter housing to throttle body. Once removed look inside on the bottom of throotle body. You will see a square shaped hole. This goes to IAC valve. Give it a good shot of carb cleaner. May have to do it more than once. Car will run rough after first started till cleaner burns off. You can check operation of valve by putting your finger over the square port. When cold you should feel strong suction. When car is warmed up you shouldn't feel it.