Scirocco 8v Idle Mixture Adjustment Procedure – Basic CIS

Scirocco 8v Idle Mixture Adjustment – w/ Basic CIS


1.  Adjust ignition timing and idle speed.
2.  Remove plug from mixture adjusting screw bore and insert a 3 mm allen wrench (tool P377 or equivalent).
3.  Adjust CO level to specifications as described on vehicle emissions label by turning mixture adjusting screw. Turn screw in to increase CO percentage or out to decrease CO percentage.


1.  Adjust ignition timing and idle speed.
2.  Shut off engine and connect electrical connectors to idle stabilizer together.
3.  Disconnect crankcase ventilation hoses at valve cover.
4.  Connect suitable dwell meter to oxygen sensor test connection (near cold start valve). Connect positive lead to oxygen sensor test connection (blue/white wire) and negative lead to ground.
5.  Zero meter and set on 4 cylinder scale.
6.  Connect tachometer.
7.  Disconnect charcoal filter hose at front left bumper.
8.  Disconnect oxygen sensor electrical connector, positioning connector so that it does not contact ground.
9.  Remove cap from probe receptacle.
10. Connect CO tester to probe receptacle, ensuring that there is no exhaust leak.
11. Start engine and adjust idle speed as necessary.
12. Dwell reading should be 48-52% steady and HC reading should be steady and under 300 parts per million.
13. Adjust CO as necessary by turning mixture adjusting screw, removing concealment plug from mixture adjusting screw bore.
14. If CO is not within specifications or HC reading fluctuates, check for
a. Leaking exhaust system,
b. Leaking intake system,
c. Uneven fuel distribution,
d. Incorrect injector spray pattern.
15. If, after connecting crankcase ventilation hose(s), meter reading drops more than 16%, fuel vapors from diluted oil (from repeated short trips) are a likely cause. An oil change may be necessary.
16. Stop engine and disconnect all testers.

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