Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Auxiliary Accelerator Pump System: Operation
When accelerating with a cold engine, the main acceleration pump capacity is insufficient to provide good acceleration. The AAP system is vacuum controlled and the VSV is open during constant RPM. Intake vacuum pulls on the AAP diaphragm drawing fuel into the AAP chamber. During acceleration, low vacuum applied to the AAP diaphragm allows spring tension to force fuel from the AAP chamber into the acceleration nozzle.
Courtesy of Toyota Motor Sales, U.S.A., Inc.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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