Checking and adjusting idle speed and mixture quality

HCS and CVH engines

Many of the engines are equipped with fuel injection systems of one kind or another, which are completely controlled by the engine management system. On most of these vehicles, there is no provision for adjusting idle speed or mixture quality without special equipment.

On carbureted and fuel injected 1.6 liter EFI engines, monitoring and adjustments are required as part of service requirements. and they are described below.

Idle speed and mixture quality, check and adjustment - engines with a carburetor

Before checking and adjusting, check that the spark plugs are in good condition and have the correct electrode gap. Adjustment requires an accurate tachometer and an exhaust gas analyzer.

Check that all electrical consumers are turned off during the following procedures.

Connect the tachometer to the engine in accordance with the manufacturer's instructions. and insert the exhaust gas analyzer probe into the exhaust pipe.

Warm up the engine to normal operating temperature before turning on the radiator fan. Remove the connector from the temperature sensor for turning on the fan and close the connector contacts with a jumper to turn on the radiator fan for constant operation (see fig. 1.11).



If present, remove the vacuum tube from the throttle.


Start the engine and increase the engine speed to 3000 rpm for 30 seconds, and repeat this three minutes later during the control/adjustment procedure.

With the throttle fully released, check the idle speed after 3-5 seconds. If adjustment is necessary, turn the idle speed screw until the desired speed is obtained.

To adjust the quality of the mixture, to access the adjusting screw, use a thin screwdriver to remove the plug from the screw. To do this, remove the air filter, while the crankcase ventilation hose must remain in place.

Turning the mixture quality adjusting screw clockwise leads to a leaner mixture, and vice versa, turning the screw counterclockwise leads to a richer mixture (see fig. 1.12).

Checking and adjusting idle speed and mixture quality - 1.6 liter EFI engines

Run the engine at high idle until the engine reaches normal operating temperature and the cooling fan turns on. Check the CO content in the exhaust gases and compare the result with the required value. To adjust the quality of the mixture, remove the plug from the adjusting screw and adjust (see fig. 1.13).




Check the idle speed by disconnecting the multi-pin plug from the idle speed control valve. Increase the engine speed to 2000 rpm and hold the engine at this speed for 30 seconds, fully release the throttle and check the idle speed.

To adjust, remove the plug with a small screwdriver, and by turning the adjusting screw, set the required idle speed. Turning the screw counterclockwise increases the idle speed (see fig. 1.14).



Reconnect the idle speed control valve multi-pin plug, and check that the engine speed, which briefly rises to 900 rpm, then drops to the specified normal idle speed.