Visual inspection

A leak in the intake system area allows unmetered air, i.e. air that is not accounted for by the control unit calculations, to enter, and therefore significantly disrupts mixture preparation. The mixture becomes uncontrollably lean. This fault is most clearly manifested by unstable idle speed. However, this same fault may also manifest as a ringing noise when the engine is running under full load.

PROCEDURE

Check that the vacuum hoses are tight and free of cracks. All hoses on the fuel mixture preparation unit or intake manifold (for example, brake booster, intake air preheating, fuel evaporation system) must be checked.

Warm up the engine and let it run at idle speed, open the hood.

Spray the fuel mixture preparation unit near the exhaust manifold flange, the intake port flange seals and the lines to vacuum-operated units with a spray can containing fuel spray (for example "Startpilot") (with the lambda sensor connector disconnected).

If the engine speed changes when a specific location is sprayed, there is a leak at that point.

Can a fuel line leak be identified?
Have the wire connectors been disconnected and reconnected many times? Corrosion or improper handling can lead to unreliable contact.

Carefully inspect the connectors of the individual injection system components. Do not bend the contacts; treat them only with spray.