DESCRIPTION
Throttle control system is used to reduce hydrocarbon (HC) emissions during gear shifting and deceleration. Throttle opener diaphragm holds throttle open slightly as necessary to improve combustion.
On Civic 1500 HF models, system consists of dashpot check valve and throttle controller. All other Civic models except CRX Si use a metered orifice to regulate vacuum to throttle controller. On all other carbureted models, system consists of a throttle controller, cranking opener solenoid valve, check valve, and dashpot check valve.
DASHPOT SYSTEM
This system slows closing of throttle. During periods of deceleration, ported vacuum in carburetor acts on the throttle control valve through dashpot check valve to hold throttle open slightly. Fixed orifice in dashpot check valve gradually decreases vacuum until the throttle closes completely.
Speed at which throttle closes is determined by size of fixed orifice in dashpot check valve, throttle return spring tension, and amount of vacuum generated at carburetor port above preset level in dashpot check valve.
THROTTLE CONTROL VALVE
This system aids engine starting. As starter is engaged, cranking solenoid valve is activated through starter relay to allow intake manifold vacuum into diaphragm. This helps to maintain correct throttle opening angle.
Scheme 17
- Connect tachometer to engine. Warm engine to normal operating temperature (cooling fan on). Disconnect vacuum hose from throttle control valve.
- Connect hand vacuum pump to throttle control valve and apply 8 in. Hg vacuum. On Civic models, disconnect vacuum hose No. 6 from throttle controller with engine idling. Engine speed should increase to 1400-2000 RPM. (Scheme 17): Dashpot System (Civic)
- On Civic models, loosen lock nut and turn adjusting nut. (Scheme 18)
- If speed cannot be adjusted, or diaphragm will not hold vacuum, replace throttle controller and retest.
