Table of contents: Cold engine does not start or starts… ↓ Warm engine does not start or starts… ↓ The engine starts but stalls again ↓ Engine vibrates at idle ↓ The engine stalls ↓
The injection/ignition systems are equipped with a fault diagnostic system. This means that any faults that occur are diagnosed and stored in the memory. This applies to "long-term" faults and faults that occur for a short time. The latter are erased after 5 engine starts if they are corrected on their own.
The faults recorded in the memory can only be determined in a workshop, since a special device is required for this. The following description will indicate some checks that can be carried out without any particular difficulties, others require special devices so that you can independently determine some faults and carry out minor repairs. The most common faults should be indicated.
Cold engine does not start or starts very poorly
The fuses may be blown. Replace them.
The voltage supply relay is faulty. Have it checked at a workshop.
The fuel pump is not working or the fuel supply is insufficient. Check the pump or replace it (a special key is required).
The fuel pressure regulator is faulty. Have the fuel pressure measured at a workshop.
The coolant temperature sensor is faulty. You can check the sensor yourself (using an ohmmeter).
The throttle control unit is faulty. The unit needs to be checked in a workshop.
The electronic control unit is faulty. This unit is also checked in the workshop.
The wiring harness between the Hall sensor and the control unit is damaged. Check it.
The engine sucks in excess air. Check all hose connections from and to the air filter.
Warm engine does not start or starts very poorly
Leaky vacuum line to fuel pressure regulator. Check it. Perform all the above checks yourself or in a workshop.
The plugs are loose. Check them.
The engine starts but stalls again
Throttle control unit malfunction. Have it checked at a workshop.
The vacuum line to the pressure regulator is loose. Check it.
Lambda probe defect. Check it in the workshop.
Engine vibrates at idle
The fault may be in the voltage supply relay or in the coolant temperature sensor, as well as in the throttle control unit itself. Check these parts.
The engine stalls
The air filter is clogged. Install a new filter.
Fuel pump fault (insufficient fuel supply).
Leaks in the injectors.
The throttle control unit is faulty. Have it checked at a workshop.
(The original version of the article is posted on the website: «AudiManual»)