Visual inspection

A leak in the intake system allows "unmetered" air, that is, air that is not registered by the control unit, and therefore significantly disturbs mixture preparation. The mixture becomes uncontrollably lean. This fault is most clearly shown by unstable idle speed.

PROCEDURE

Check the vacuum hoses for tight fit and cracks. All hoses on the intake manifold (for example, brake booster, intake air preheating, evaporative emission solenoid valve) must be checked.

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

Spray the throttle body housing, the sealing of the intake manifold flanges and the lines to the vacuum-operated components with a spray containing fuel spray (for example "Startpilot") (disconnect the plug connector from the lambda sensor).

If the engine speed changes when spraying a specific area, 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 poor contact.

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