Idle Speed & Mixture

NOTE: On vehicles with fuel injection, idle mixture is controlled by the Electronic Control Module (ECM). Idle mixture adjustment is not required or possible on fuel injected models. On carbureted models, mixture should be adjusted only if vehicle fails emission testing or carburetor has been disassembled.

NOTE: Ensure idle speed and timing are set prior to adjusting idle mixture. If mixture adjustment exceeds 3 minutes, run engine at 2000 RPM in NEUTRAL for one minute, and resume adjustment.

CURB IDLE & IDLE DROP

Application

RPM

4.2L

Curb Idle

⁽¹⁾ 680 (50 State)

Idle Drop

5.9L

Curb Idle

600

Idle Drop

⁽¹⁾	700 RPM (High Altitude)

NOTE: If final RPM differs more than 30 RPM from specified curb idle, reset curb idle, and repeat mixture adjustment.