Chrysler Front Wheel Drive Cars 6-CYL 1988-1995 Repair Information

Idle Speed and Mixture Adjustments


Since all of the vehicles covered by this information utilize electronic fuel injection systems, the idle speed and mixture settings are controlled by the vehicle's computer. These engine controls are essentially unadjustable.

On the 3.0L (90° V6) engines found in Premier and Monaco vehicles, the idle speed regulator allows a controlled amount of air from the air cleaner to reach the intake manifold during closed throttle conditions to maintain engine idle. The inlet side of the regulator is connected to the air cleaner bonnet, while the outlet side is connected to the throttle body adapter below the throttle plate by a hose.

The idle speed regulator consists of a permanent magnet motor that operates a vane type valve. The ECU (Electronic Control Unit) controls the amount of air routed through the regulator by opening and closing the valve. Voltage is supplied to the idle speed regulator through the B+ Latch relay, while the ECU controls the ground path to extend or retract (open or close) the valve.

On the 3.0L (90° V6) on all except Premier and Monaco models, 3.3L and 3.8L engines utilize an idle air control motor. The idle air control motor is mounted on the throttle body and is controlled by the PCM (Powertrain Control Module). The PCM adjusts engine idle speed through the idle air control motor to compensate for engine load or ambient conditions.

The throttle body has an air bypass passage that provides air for the engine at idle (the throttle blade is closed). The idle air control motor pintle protrudes into the air bypass passage and regulates air flow through it.

The PCM adjusts engine idle speed by moving the idle air control motor pintle in and out of the bypass passage. The adjustments are based on inputs the PCM receives. The inputs are from the throttle position sensor, engine speed sensor (distributor pick-up coil), coolant temperature sensor, and various switch operations (brake, park/neutral, air conditioning). Deceleration die out is also prevented by increasing airflow when the throttle is closed quickly after a driving (speed) condition.