Checking the intake air heating (VW Passat B3)

Carburetor 2E3 and Mono-Jetronic system

The intake air preheating is controlled by an air damper in the air filter box depending on the load and temperature. The air damper is controlled by a vacuum diaphragm mechanism using the vacuum created in the intake manifold. The temperature regulator in the intake air guide casing above the carburetor controls the vacuum depending on the temperature and vacuum in the intake manifold. If the intake air preheating 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 "4" (near the air filter housing) to temperature controller "3" (in the air intake guide housing of the carburetor) and from the temperature regulator to the carburetor.

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



Disconnect the hose with the brown connection from the temperature regulator in the guide casing and check the operation of the air damper by sucking through your mouth. The damper should close and open audibly.

If the damper remains closed, check the ease of movement of the air damper and, if necessary, ensure its mobility.

If no fault is found, replace the vacuum diaphragm mechanism.

[The text is copied from this portal: vwmanual.ru]

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.

Connect both vacuum hoses to the temperature controller. Vacuum hose connector from the vacuum diaphragm mechanism (brown connector) may have the following identification features: a brown sticker next to the nipple; brass fitting at the temperature regulator; the fitting has a slot.

Start the engine and let it idle. The control valve should tighten (cold air vent blocked).

Remove the black vacuum hose from the temperature controller (to the carburetor). The control valve should return to its original position within no more than 20 seconds.

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

Install the air filter, see below.