Visual inspection

PROCEDURE

First, check the air ducts for leaks! All hoses must be inspected, from the thick air intake hose to the thin vacuum hoses.

Are the sealing gaskets of the injectors, as well as the intake manifold flange gaskets, in good condition?
Leaking points allow unmetered air, that is, air that is not registered by the system and therefore significantly disturbs mixture preparation. The mixture becomes uncontrolled lean. This results in engine malfunctions, manifested primarily as rough idle.

Warm up the engine to operating temperature, then let it run at idle, open the hood, and disconnect the electrical connector of the lambda sensor.

Spray the intake manifold flange gaskets and other suspect components with starting fluid (e.g., "Startpilot") from an aerosol can.

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

Can fuel line hoses leaks be identified?
Have the wire terminals been disconnected and reconnected multiple times? Corrosion or improper handling can lead to insufficient contact.

Carefully inspect the connectors of the individual fuel injection system components. They may only be treated with contact spray, but must never be bent, as this may cause malfunctions.