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.
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HOMESERVICE MANUALSCHEVROLET1966CHEVELLE BASE, 2D CONVERTIBLE, 5.3L ENG, AUTOMATIC TRANS, TRANS MFR CD THM400REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETUNE-UPEXHAUST EMISSION SYSTEMS - TUNE-UPIDLE SPEED & MIXTURE ADJUSTMENTTACHOMETER LEAN DROP PROCEDURE (PREFERRED METHOD)ALL MODELS (1974)
1966 Chevrolet Chevelle Base, 2D Convertible, 5.3L Eng, Automatic Trans, Trans Mfr CD THM400
All Models (1974)
1966 Chevrolet Chevelle Base, 2D Convertible, 5.3L Eng, Automatic Trans, Trans Mfr CD THM400SECTION All Models (1974)
- Firmly set parking brake and block drive wheels. Disconnect fuel tank vent hose from vapor canister, on Corvette only, remove fuel tank filler cap. Disconnect and plug distributor vacuum advance hose at vacuum advance unit.
- With engine at normal operating temperature, air conditioning "OFF" (if equipped), place transmission selector lever in "D" (if automatic) or Neutral (if manual shift).
- Break off tab on mixture cap using suitable tool. Adjust idle RPM to higher of two idle speeds given in Lean Drop Idle Speed specifications, with idle stop solenoid energized and extended.
- Equally richen (turn counterclockwise) mixture screws until maximum idle speed is achieved. Reset speed if necessary to higher specified idle speed.
- Equally lean (turn clockwise) mixture screws until lower specified idle speed is obtained (Example: 650/600 RPM). Reconnect fuel tank vent hose and distributor vacuum advance hose. Reinstall fuel tank filler cap on Corvette models.
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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.