Checking idle speed and exhaust gas analysis

The illustration shows the connector disconnected from the idle air control valve (arrow) in order to check the valve and the wiring to it.

Throttle cable mounting on engine with 85 kW output; numbers denote: 1 and 4 – clamps; 2 – accelerator cable; 3 – connector protection; 5 – accelerator cable sheath locking segment.

The Digifant injection system does not require adjustment, because the system is self-learning. This means that the control unit corrects the idle speed as necessary. The so-called basic adjustment is performed only in doubtful cases. It is not carried out by turning the adjusting bolts, but with the previously mentioned fault memory reader V.A.G 1551, after the fault memory has first been read. Specified values for idle speed or CO content at idle (test conditions: engine at operating temperature, all electrical consumers switched off and ignition timing correctly set) are:

Idle speed: 850 ± 50 rpm.

CO content test in exhaust gas: 0.6–1.0 % (measured at the CO measuring tube).

If you obtain different values, check the vacuum hoses and the fuel evaporation control solenoid valve, and read the fault memory.

Note: for everything you need to know about exhaust gas analysis, checking the catalytic converter, checking the lambda sensor and the accelerator cable, refer to the previous chapter “Mono-Motronic Injection System”.

Routine checking of the catalytic converter and lambda sensor is performed in a workshop, as described in the section Checking the Catalytic Converter and Lambda Sensor for the Mono-Motronic Injection System.