Took the car in for biannual emmissions. Slightly higher CO, HC than 2 years ago, seemed to be running rich.Passed OK, but Hooked up the Voltmeter and go a 5.5v average-spec says 2.4 to 4.8v or so. Book also says that lean=higher voltage, rich =lower number. I should have been lean, why did I get a "rich" (higher HC & CO) symptoms but showed lean? Does this number get effected by altitude? I live @ 6000ft, I am told the altitude sensor leans out the mixture, but how? Any ideas on how to figure out? Are there corresponding Duty Cycle numbers instead of voltages? Thanks Scott BTW Does Lambda fluctuate much off idle? Under load? If so, whats normal?