Idle Speed and CO Content, Checking and Adjusting

Idle Speed and CO% Checking and Adjusting

Note: It is important to follow the sequence when performing idle checking/adjusting.

1 Check timing, adjust if necessary
Temperature sensor II disconnected
RPM: 2000 - 2500

2 Check idle speed and CO content, adjust if necessary
Idle stabilization valve disconnected (with ignition off)
Disconnect oxygen sensor (with ignition off)

Note: If the oxygen sensor is disconnected while the ignition is ON the system will maintain the fuel mixture based on the last good oxygen sensor reading in memory.The oxygen sensor must be disconnected with the ignition off, to cancel the memory in the Electronic Control Unit (ECU)

Test And Adjustment Conditions

- Engine oil temp min. 80°C (176°F)
- All electrical consumers turned off (radiator fan should not be running while performing checks or adjustments)
- Crankcase breather hose removed from oil vent and plugged
- Throttle valve switch operating properly (closed when in idle position)
- Ignition timing within specifications
- Idle stabilizer operating properly (with ignition turned on, valve should vibrate and hum)





- Charcoal cannister hose to the air filter must be pinched closed. See arrow

Connecting Test Equipment

WARNING: Ignition must be turned off when connecting test equipment





- Connect VW 1367 tester for ignition timing and rpm display function
- Using adapter VW 1473, connect tester VW 1367 to terminal 1 of ignition coil





- Connect CO tester to adapter on left exhaust pipe, using Sun tool 120.239 or equivalent

Work Procedure:





- With ignition switched off, disconnect oxygen sensor connector (1) and idle stabilizer control valve connector (2)





- Check idle speed rpm, correct if necessary using adjusting screw (1)
specification: 880 ±50 rpm
- Check CO content
specification: 0.7 ±0.4% vol.

For CO adjusting, remove screw cap as follows:
- Drill CO adjusting screw cap using 2.5mm (0.098 in) drill
- Thread 3mm (0.137 in) sheet metal screw into drilled hole
- Grasp screw with pliers, pull out cap
- Set idle speed and CO content by alternately turning adjusting screws (1 and 2) to obtain specifications
- Reconnect oxygen sensor connector and idle stabilizer control valve connector
- Let engine idle approx. 2 minutes
- Check CO content, correct if necessary by repeating adjusting procedure





Check oxygen regulation function as follows:
- Remove hose (1) from pressure regulator (2) and plug
CO should increase briefly, then drop in value.
- With ignition switched off, disconnect oxygen sensor
- Restart engine, let idle
CO content should correspond to chart according to elevation of workshop

Note: CO content is altitude dependent, refer to the following chart to compensate for the altitude of the workshop.





- With ignition switched off re-connect oxygen sensor
- Restart engine, let idle
CO content must read within specifications:
0.3 to 1.1% (not dependent upon elevation with sensor connected)
- Adjust if necessary
- Secure CO adjusting screw with new safety cap

Note: After adjusting, the hoses for the crankcase must be reconnected. If the control current and the CO content change, this is not due to an improper adjustment, but rather to oil dilution caused by short distance driving. With long distance drives, the amount of fuel in the oil will be reduced and the CO value will normalize again. A short-term solution would be an oil change.