Throttle Valve Basic Adjustment

The factory-set throttle valve adjusting screw is not used to adjust idle speed. Its only function is to provide a mechanical stop for the linkage to prevent damage to the throttle plate and housing. It should be adjusted only if the factory setting has been changed.

To check the adjustment, disconnect the vacuum line from the carbon canister control valve (see Fig. 7-5 shown later), and connect a vacuum gauge in its place. At idle there should be approximately zero vacuum. Up to 1 in. vacuum is acceptable. If the vacuum gauge measures greater than 1 in. at idle, the throttle valve basic adjustment should be corrected.

To correct a faulty throttle valve adjustment, loosen the locknut and back off the throttle valve adjusting screw until there is clearance between its tip and the throttle valve lever.

See Fig. 7-4. Place a thin piece of paper between the screw and the lever and turn the adjusting screw in. When the screw is just barely gripping the paper, remove the paper and turn the screw in an additional 1/2 turn. Tighten the locknut.

Fig. 7-4.

Throttle valve adjusting screw (2) and locknut (1). Set by contact (arrow) with throttle valve lever.