Checking and Adjusting Engine Idle Speed and CO Level

EVERY 2 YEARS OR EVERY 20,000 KM (12,000 MILES)

* The engine must be warmed up to normal operating temperature, with ignition timing correctly set and valve clearances adjusted (where adjustable). The air filter must be in good condition, and all electrical components (including the air conditioning system, where fitted) must be switched off.

Gasoline Engine

PROCEDURE
1. Connect a tachometer and CO meter to the engine. Mechanics use a special CO tester whose probe is inserted into the exhaust pipe, but a standard tester inserted into the tailpipe can also be used. However, note that on models with a catalytic converter, correct CO readings cannot be obtained from the tailpipe.
2. Idle speed cannot be adjusted manually, because the idle air control valve is actuated by the electronic control unit. If the idle speed does not correspond to the values given in Specifications at normal engine operating temperature, check the intake air system for leaks and check the operation of the idle control valve.
3. Compare the CO meter readings with the values given in Specifications. If adjustment is required, remove the plug from the air flow meter and turn the adjusting screw until the required value is obtained (on some models a hex key may be required). Finally, install a new protective plug.

Diesel Engine

The most difficult problem when adjusting idle speed is connecting a tachometer, since tachometers available on the market are designed for connection to the ignition coil of a gasoline engine. The required idle adjustment can be achieved provided the valve clearances and fuel injection timing are correctly adjusted.

Diesel idle speed check is performed as follows:

PROCEDURE
1. Start the engine and warm it up to operating temperature. Switch off all electrical consumers. If equipped with an automatic transmission, shift the transmission into Neutral.
2. Start the engine and check its speed using a tachometer or judge it by ear. Uneven engine operation is felt immediately.
3. If engine speed is outside the Specifications, use a screwdriver to turn the adjusting screw so that the engine runs smoothly at idle. To increase speed, turn the screw in. The throttle control lever moves outward at this time.
4. Holding the adjusting screw with a screwdriver, tighten the locknut.