But 1987 car passes today's emissions tests. Granted, that a finer time scale of mixture adjustment will produce less emissions. I think like any other feedback system, it is not always easy to pin point the problem to a single component and when one of the components is the computer and the other is the O2 sensor, we have to pick the O2 sensor for replacement. Atleast in my car which has a mechanical fuel injection system, the other problem is the baseline air/fuel ratio, the computer/O2 feedback system can only make fine adjustments not anything coarse. So even if the output of the O2 sensor would appear to remain constant, nothing may be wrong with the computer/O2 feedback system.

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Saumil S. Patel