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Connect tachometer to engine. Run engine until normal operating temperature (cooling fan on) is reached. Disconnect vacuum hose from throttle control valve.
Connect hand vacuum pump (except Civic models) to throttle control valve and apply 8 in. Hg vacuum. Check that engine speed rises (within one minute) to 1500-2500 RPM on Accord and Prelude models. On Civic models, disconnect vacuum hose No. 6 from throttle controller with engine idling. Engine speed should increase to 1400-2000 RPM.

Fig 1: Dashpot System (Civic)
Courtesy of AMERICAN HONDA MOTOR CO., INC.
On Accord and Prelude models, if RPM was too low, widen adjusting slot in throttle control valve lever using screwdriver. See Fig 2 . If RPM was too high, narrow slot with pliers. On Civic models, loosen lock nut and turn adjusting nut. See Fig 3 .
On all models, if speed cannot be adjusted, or diaphragm will not hold vacuum, replace throttle controller and retest.

Fig 2: Control Lever Adjusting Slot Location (Accord Shown; Prelude Similar)
Courtesy of AMERICAN HONDA MOTOR CO., INC.

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.

Safety Warning

Dashpot System Check