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20R engine (carbureted)
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* May 31, 2007, 05:38:33 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.

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79 Corona


* May 31, 2007, 10:26:12 PM
#1
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.

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2002 Corolla S, Silverstream, 1.8L 1ZZ-FE (VVT-i)
2003 Matrix XRS, Cosmic Blue, 1.8L 2ZZ-GE (VVTL-i) - RIP
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* June 14, 2010, 09:57:58 PM
#2
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 couldn\'t 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.

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* June 15, 2010, 11:17:01 AM
#3
I put a Weber carb on mine.

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79 Corona


* June 19, 2010, 03:41:05 AM
#4
figured out the problem was a clogged fuel filter.  i\'ll have to check on the weber carb

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