Checking and adjusting engine idle speed (VW Passat B4)

Before adjusting and checking the engine idle speed, the following must be done:

• warm up the engine (oil temperature not less than 80°C);
• turn off electrical consumers, including air conditioning, if installed;
• make sure that the idle and full load switches or the throttle position sensor are in good technical condition (the ignition timing and crankshaft speed should change when the switch or sensor connector is disconnected);
• make sure that the ignition timing and spark plug gap are set correctly;
• make sure the electromagnetic valve is working properly: when the ignition is turned on, the valve should vibrate and hum.

The electric fan of the cooling system should not be switched on during the check. Connect the control tachometer according to the operating instructions, connect the gas analyzer to the tube A (fig. 2-100) measuring the carbon monoxide (CO) content in the exhaust gases. Disconnect the crankcase ventilation hose B (Fig. 2-100 on the "RV" engine) or 3 (Fig. 2-103 on the "2E" engine) and plug it. Start the engine at idle speed and let it run for about 1 minute. Disconnect the blue connector 2 (fig. 2-101) coolant temperature sensor, then increase the crankshaft speed three times to a value greater than 3000 rpm and leave the engine idling. Check the crankshaft speed at idle and the CO content in the exhaust gases, which should be within 750-850 rpm and 0.5-1.5%, respectively. If the obtained values are not within the specified limits, remove the plugs from the idle adjustment screws and, alternately turning the idle air screw (to adjust the idle speed) and the CO correction screw (fig. 2-102 and 2-103), achieve the required values.











After adjustment, connect the crankcase ventilation hose and connect the coolant temperature sensor connector of the fuel injection control subsystem, install new plugs on the idle speed adjustment screws. Press the accelerator pedal several times and check the idle speed again, which should be within the required limits.


Disconnect the fuel pressure regulator vacuum hose from the throttle body pipe and close the pipe opening. The CO content should first increase briefly and then decrease. Then reconnect the hose.

Note: On the "2E" engine with a catalytic converter of exhaust gases, the engine crankshaft speed at idle and the CO content are automatically maintained within the specified limits by commands from the controller.