Fast Idle Thermo Valve - Honda Prelude 1993 Service Manual

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Fast ldle Thermo Valve

To prevent erratic running when the engine is warming

up, it is necessary to raise the idls speed. The fast idle

thermo valve is controlled by a thermowax plunger.

When the engine is cold, the engine coolant surround-

ing the thermowax contracts the plungef, allowing ad-

ditional air to be bypassed into the intake manifold so thst

the engine idles faster. When the engine reaches ope.-

ating temperature, the valve closes. reducing the amount

of air bypassing into the manitold.

H23A1 engino (USA: Si/Canada: SR),

H22Al 6ngin€ (USA: Si VTEC/Canada: SR-V)

NOT€: The fast idle thermo valve is factory adiusted;

it should not be disassembled.

1. Remove the intake air duct from the throttle bodv.

Stan the engine.

Put your finger over the lower port in throttle body

and make sure that there is air flow with the engine

cold {engine coolant temperature below 860F,

thermo valve and

(1.2 kg-m, 9 lb-ttl

4. Warm up the engine (the radiator fan comes on).

Check that the valve is completely closed. lf not,

air suction can be telt at the lower gort in the throt-

a lf any suclion is felt, the valve is leaking. Check

engine coolant leveland forair in the engine cool-

ing system (see section 1O).

lf OK, reDlace the tast idle thermo vslve and

Troubleshooting