Checking Intake Air Preheating

Models with 4-cylinder engines
PROCEDURE

The temperature regulator is located in the air filter housing. Its hose connections are accessible on the engine with Mono-Motronic injection from the underside of the air filter housing.

Disconnect the hose from the brass fitting or the fitting marked accordingly.

Draw air strongly out of the hose with your mouth: the warm air flap must open or close audibly.

If this does not occur: check the valve for free movement, and check the hose and the diaphragm of the vacuum ignition timing advance unit for leaks.

Then check the temperature regulator. During the check, the air temperature must be below +20 °C.

Disconnect the hose fitting to the air flap at the temperature regulator or at the warm air valve.

Disconnect the hose fitting to the engine at the fuel mixture preparation unit or at the throttle body housing.

Draw air strongly out of the hose with your mouth: the hose must be open (passable).

Warm the temperature regulator above 45 °C with a hair dryer. Draw air strongly out of the hose again: now it must be closed.

If not, replace the temperature regulator.

Models with 5- and 6-cylinder engines
PROCEDURE

Remove the air intake hose behind the headlight cover.
Look into the hose connection and, if necessary, illuminate it with a flashlight.

Depending on the ambient temperature (see previous section), the air flap must shut off access of cold or warm air.

After removing the air supply hose on the 5-cylinder engine, the intake air preheating valve (2) is visible. Directly next to it is the thermal element (1) that actuates it. Position (3) shows the warm air hose leading to the exhaust manifold.

Left: the illustration shows the air filter housing removed and set aside in the engine compartment. The vacuum ignition timing advance diaphragm unit with the warm air flap (2) is unscrewed from the filter housing, the vacuum hose (arrow) is still connected:

1 – cold air intake connection;
3 – warm air hose.

Right: the intake air preheating temperature regulator (2) is located in the air filter housing cover on the 85 kW engine. Position (1) indicates the vacuum hose leading from the engine.