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Re: Freqs on O2

I've used both these techniques on my car and they're both useful. I'd point
out one thing - old Oxygen sensors can fail by getting "slow", so even though
you see them going up to ~ 0.8 V as you tweak the mixture screw, their
response is such that they're unable to keep the mixture correct under
load/throttle conditions. Also the duty cycle of the freq valve can be
under the same circumstances for the same reason - it looks like it's doing
it's supposed to, but you still get transient mixture problems.

Yes, very true.......  But, there are only two tests for the freq valve and
both don't need to reference the O2 sensor:  1) at idle and using the full
throttle switch closed, but car at idle speed......  An O2 that isn't working
will stall the car in every day driving, a slow O2 will not throw off the
freq valve test necessarily....  To get the lowdown, a fuel meter readout
(lots of archives on these) is the way to fly....  Really if that is
functioning properly, readings off on the O2 and the Freq valve are really
irrelevent......  Audi makes the tech procedure pretty simple, if you set the
idle freq valve and just check the full throttle, you will pass emissions
(theoretically gives you the lowest CO)....  Yes the default is that your O2
is good......  Does it have to be perfect and speedy .....  Me thinks