Cold engine large rpm drop Fully warmed engine rpm drop

A good quick check for the wax type air valve is to observe engine rpm throughout the warm up cycle. Look for high rpm upon initial startup and gradual reduction to normal curb idle speed as the engine reaches normal operating temperature.

On D type EFI, the valve operation can also be checked by removing the air inlet pipe at the throttle body and blocking the fresh air port inside the throttle bore. When the engine is cold, engine rpm should drop greater than 100 rpm. Once the engine reaches normal operating temperature (— 176'F), rpm drop should not exceed 100 rpm.

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