DESCRIPTION
All throttle body fuel injected models are equipped with an Automatic Temperature Control (ATC) air cleaner assembly. This device maintains temperature of air entering throttle body within a constant range. This provides leaner air/fuel mixture to reduce harmful exhaust emissions.
In addition, the ATC air cleaner improves engine warm-up characteristics and helps prevent throttle body icing. The ATC air cleaner assembly consists of an air cleaner housing, vacuum motor, temperature sensor, air control valve, hot air duct, fresh air duct, and various connecting hoses.
Scheme 9
ATC SYSTEM
The ATC air cleaner is controlled by inlet air temperature and load condition of engine. The inlet air temperature is detected by temperature sensor, and vacuum motor is activated by intake manifold vacuum.
Cold Engine Operation
When engine intake air temperature is below 100°F (38°C) sensor air bleed valve is closed. This allows intake manifold vacuum to vacuum motor. With vacuum applied to vacuum motor, air control valve, attached to vacuum motor diaphragm, is opened. This allows hot air into air cleaner through hot air duct on exhaust manifold.
Hot Engine Operation
When engine vacuum is low, or when engine is under a heavy load, the air control valve opens (regardless of temperature) to allow cold air induction for increased engine power.
- If engine stall, hesitation, increase fuel consumption or lack of power is experienced with vehicle, check all vacuum lines for connection, cracks or loose fitting and proper routing. Replace or reroute as necessary.
- To check vacuum motor, stop engine and unhook fresh air duct. Using a mirror, check position of air control valve inside duct. With engine warm, fresh air inlet should be open and hot air duct closed. Check control valve linkage.
- Disconnect vacuum motor inlet vacuum hose. Install another length of hose to inlet and apply vacuum through this hose to vacuum motor.
- With vacuum applied, again use mirror to check air control valve position. Fresh air inlet should now be closed and hot air inlet open.
- With hot air inlet open (vacuum still applied), pinch vacuum hose to cut off air to vacuum motor. Air control valve should hold position for more than 30 seconds.
- If force of diaphragm spring overcomes vacuum and opens fresh air inlet in less than 30 seconds, replace vacuum motor assembly.
- To check temperature sensor, start and idle engine. As engine warms up, air control valve should slowly open to admit fresh underhood air. Ensure that air control valve moves up and down with increase or decrease in engine speed.
Scheme 10
Vacuum Motor
Disconnect inlet vacuum hose at vacuum motor. Connect vacuum pump hose at inlet. Apply 1.97 in. Hg vacuum, air control valve should start to open. Apply 3.94 in. Hg vacuum, air control valve should fully open. If air control valve does not operate as specified, replace air control valve.
Temperature Sensor
With engine cool and idling, disconnect inlet vacuum hose at vacuum motor and ensure intake manifold vacuum is present at end of hose. If vacuum is not present or weak, check vacuum hose for leaks. If no leaks are found in vacuum hose, replace temperature sensor. After engine is warmed, ensure no vacuum is present. If vacuum is present, replace temperature sensor.