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20R engine (carbureted)
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May 31, 2007, 5:38:33 PM
I have a 1979 Corona and am wondering if anyone has a good handle on the problem with the Auxilary Accelerator Pump (AAP) problem, and can provide details about it. Thanks.


May 31, 2007, 10:26:12 PM
A pretty common problem on early Toyota with the 20R engine - like the Celica, Corona, Truck.

Failure mode is usually when the diaphragm, in the auxiliary accelerator pump, in the carburetor. The AAP is designed to allow a longer accelerator pump stroke when cold.

A failed diaphragm will result in very high CO emission due to sucking gasoline straight through the accelerator pump circuit. First thing I would check would be the manifold and gasket at #4 runner (location of EGR valve) for leaks.


June 14, 2010, 9:57:58 PM
i have a 1978 corona 20r engine. just recently got it running. vacuum hoses were mismatched. i need a detailed diagram if anyone knows where i could find one. the one in chiltons manual is small and i couldnt make sense of it. is there a simple way to do get rid of all these vacuum hoses . maybe change the carb and rotor. also, i have put about a thousand miles on it since i got it running and now when i hit the accelerator pedal, its like it takes gas from the carb. however when it is idling it purrs like a kitten.


June 15, 2010, 11:17:01 AM
I put a Weber carb on mine.


June 19, 2010, 3:41:05 AM
figured out the problem was a clogged fuel filter. I'll have to check on the weber carb



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