Toyota Corolla CSi hatch revving too high
--the choke cable or the choke linkage on the carburetor is sticking, holding the revs too high.
--the gas pedal linkage, the pedal cable, or its linkage to the carburetor are sticking.
--the engine computer (if it has one) is failing, or has poor connections, or isn't grounded properly.
--various other sensors (if you have them) could be failing.
--the mechanism (computerized or mechanical) calling for more fuel to the carburetor when the air conditioning (if you have it) is turned on could be sticking or not working properly.
You should be able to test most of these possibilities while the car is standing still, with the engine running. Start with the choke -- have a helper move the knob and see if the engine responds properly, especially in the "off" position. Then have the helper operate the gas pedal while you watch what's going on with the carburetor.
Have your helper turn the a/c on and off. If you see a mechanical linkage to the carburetor move when the a/c is turned on, it should move back to its original position when it's turned off.
If any of these linkages (including the gas pedal linkage under the dash) are sticking, try spraying the affected area with a lubricant (like WD-40). If that doesn't help, spray lubricant into the cables, or replace them.
If all else fails, carefully check all vacuum lines in the engine compartment. An intermittent leak (or blockage) could be affecting engine speed.
on Feb 09, 2018