With strobe light:

WARNING: This page does not describe the selected car, but rather 27 other vehicles, including the 2002 Volkswagen Cabrio, 2001 Volkswagen Cabrio, 2000 Volkswagen Cabrio, 1999 Volkswagen Jetta, and 1999 Volkswagen Golf. However, it is still accessible from the selected car via links, so may be relevant.

Aim strobe at ignition timing notch.
Adjust ignition timing, if necessary, by turning distributor.
Run engine at idle for at least one minute.
Check idle speed and CO content.
NOTE: Idle speed and CO content cannot be adjusted. If deviation from specification exists, make the necessary repairs.

Fig 1: Locating Ignition Timing Notch (Engine Code: ABA)
Courtesy of VOLKSWAGEN OF AMERICA, INC.
Press --> button (coolant fan must not start).
Press buttons -0- and -6- to select "End Output" function 08, and press -Q- button to confirm input.
Test operation of three way catalytic converter (THREE WAY CATALYTIC CONVERTER (TWC) ).
Refer to notes on THREE WAY CATALYTIC CONVERTER (TWC) after completing emission and idling test.