Engine Performance - Erratic Running/Lean Mixture

87VW2

GROUP

97
NUMBER

87-08 December 21, 1987
MODEL(S):

Jetta, Quantum, all m..y.
SUBJECT:

Erratic running condition/ lean mixture
A lean running condition can be caused by stray voltage affecting the oxygen sensor signal.

To determine if stray voltage is present:

^ Disconnect the oxygen sensor lead (engine off).

^ Turn on the ignition (do not start engine).

^ Measure for voltage between the green lead of the disconnected oxygen sensor and the ground connection at the cold start valve: Voltage should not be more than .55VDC (residual voltage for electronic circuitry).

If more than .55 volts is present:

^ Clean the grease from the fuel injection control unit plug using rubbing alcohol and allow to air dry.

^ Reconnect the plug to the control unit.

^ Repeat stray voltage test.