Checking the intake air heating (VW Passat B3)

Digifant, K-Jetronic, KE-Motronic (Mono-Jetronic see above)

The intake air heating is regulated by the air damper in the air filter box depending on the load and temperature. The air damper is controlled by a vacuum membrane mechanism using the vacuum formed in the intake manifold. The temperature regulator in the air filter box controls the vacuum depending on the temperature and vacuum in the intake manifold. If the intake air heating is disrupted, the following complaints about the engine operation may arise:

• Poor engine idling performance during warm-up;
• Transient faults;
• Insufficient power, maximum speed not reached;
• High fuel consumption.

Checking the air damper drive

Check the strength of the vacuum hoses from the membrane box (front right near the air filter housing) to the temperature controller (on top of the air filter housing) and from the temperature regulator to the intake manifold.

Check the hoses for damage and porosity by bending them and replace the hoses if necessary.



Remove the upper part of the filter together with the filter element and check the position of the control flap in the lower part of the filter. The flap should close the warm air pipe "1". Check the mobility of the control flap, if necessary, ensure its mobility.



Disconnect hose -3 - from the temperature regulator at the top of the air filter box and check the operation of the air damper by sucking through your mouth. The damper should open and close audibly. If necessary, replace the leaky vacuum membrane box.

Checking the temperature controller

Prerequisite for checking: the intake manifold must be OK, the engine must be permissibly hot to the touch. Maximum intake air temperature +20°C.

Remove the upper part of the air filter together with the replaceable filter element, see below.

The information is presented on the website (VWmanual.ru)

Connect both vacuum hoses to the temperature controller. The vacuum hose connection fitting from the vacuum diaphragm mechanism may have the following identification features: a brown sticker next to the fitting: a brass fitting at the temperature controller: the fitting has a slot.

Start the engine and let it idle. The control valve should tighten within 20 seconds (cold air hole "3" is closed, see Figure 24-233).

If the intake air temperature is between +20°C and +30°C, the air damper should be located between both pipes "1" and "3". At intake air temperature above +30°C, the air damper should completely close the intake air pipe.

Otherwise, clean the 2 holes of the temperature regulator on the inside of the air intake guide casing or, accordingly, replace the temperature regulator.

Install the air filter, see below.