Checking the thermo-pneumostatic valve (VW Passat B3)

The vacuum in the distributor ignition advance regulator is controlled by a thermo-pneumostatic valve. This means that when the engine is cold (at a temperature below about +46°C), the vacuum, thanks to the jets in the vacuum hoses, is formed quite slowly, and the ignition timing at high engine load (high vacuum in the intake manifold) will shift in the direction of advance not very much. A faulty valve reduces the power of a cold engine. Routing of hoses and location of the thermo-pneumostatic valve see above.

Examination

Remove the valve from the air damper control device and heat or cool it in a bath of water.

Blow through the valve with your mouth. At temperatures above approximately +46°C the valve should be open and allow air to pass through.

Cool the valve to a temperature below +30°C. Repeat the check. The valve must be closed, otherwise it must be replaced.