Idle Speed: Testing and Inspection

Idle speed and CO content, checking/adjusting

CAUTION! Ignition timing, CO content and idle speed RPM's are inter-related and must be checked/adjusted together.

NOTE: The Oxygen sensor remains connected during checking/adjusting.

Requirements
- engine oil temperature 80°C (176°F) minimum
- all electrical consumers switched OFF (do not take measurements while radiator cooling fan is running)
- A/C switched OFF
- ignition timing OK
- idle stabilizer valve OK, (when ignition is switched on the valve must buzz and hum)
- exhaust system must be leak tight

Checking/adjusting




- switch OFF ignition
- connect VAG 1367 engine tester using inductive pickup VAG 1367/8 on ignition coil high tension lead
- connect SUN 105 CO tester (or EPA approved equivalent) to CO tap tube using hose adaptor VAG 1363/3

CAUTION! Hose must fit securely on CO tap tube to avoid measuring inaccuracies due to dilution or leakage.




- disconnect crankcase ventilation hose from emission control valve (arrow 1) and route such that only fresh air is drawn in
- start engine and let idle
- will run from 1 to 4 minutes at increased engine RPM

When idle speed is reduced approx. 100 RPM
- disconnect blue coolant temperature sensor harness connector

CAUTION! Do not start engine with coolant temperature sensor disconnected. The control unit will go into open loop making accurate adjustment impossible.

- raise engine speed in excess of 3000 RPM 3 times then let idle




- check idle speed and CO content
- idle speed must be 800 ± 50 RPM
- CO content must be 0.7 ± 0.4 volume %

If NO
- adjust by alternately turning adjustment screws (arrows) until both specifications are obtained
- reconnect blue coolant temperature sensor
- raise engine speed 3 times then let idle
- check CO content
- must be 0.7 ± 0.4 volume%

If NO
- check OXS control, Testing and Inspection
- after repairs or replacements have been performed, install new plug over CO adjustment screw


NOTE: After adjusting the idle speed, reconnect the crankcase ventilation hose. If the CO content then changes, this is not due to improper adjustment, but rather to oil dilution caused by short distance driving and insufficient warm-up. With longer distance driving, the amount of fuel in the oil will be reduced and the CO will normalize again. A short term solution would be an oil change.