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Re: 86 5kTQ breakup/tuning problems

   Is "Frequency Valve" the idle stabilizer or the fuel distributor's 
   differential pressure regulator? The stock wiring harness has the signal 
   from the idle stabilizer located at the coil, so I'll guess you mean that 

The earlier CIS (and I suspect all "CIS" variants) Frequency Valve is the
rapidly-cycled "bypass" valve mounted on/by the master fuel distributor,
and used to "modulate" the system fuel pressure (thus effecting control
over the mixture). It's used as a "correction" signal to an otherwise
purely mechanical fuel injection system (i.e., the meter plate in the
air flow directly and mechanically controls the fuel flow to the injec-
tors). Normally, it makes a high-frequency "buzzing" sound, clearly audi-
ble. It should have a fuel inlet and outlet, and a two-wire electrical
connector. It should be the only such "thingie" anywhere near the master
fuel distributor.

It has nothing to do with idle stabilization (although for all I know
the idle stabilizer works with a substantially-identical control). How
does the idle stabilizer work? (On the UrQs, the idle is controlled
(loosely at best) by the ECU dicking around with the engine timing, and
hoping you have the base mechanical idle set more or less correctly,
and have payed obeisance to the appropriate deities.)

   Agreed- closed-looped measurement of O2 sensor voltage would show any
   mixture abnomalities. What would be an inexpensive way to determine the 
   DC offset (average mixture) of the bouncing reading? Cap and resistor?
   This is one area of measurement where I would like to use those analog
   meters (with the high-impedance front end, of course) so I can read the
   min/max bounce myself and also see dynamic trends.

   Those LED bargraph O2 sensor meters do that compensation, right?

In essence. They respond fast enough to give you a meaningful reading,
as opposed to "handheld meters" which try to average...and are basically
useless on a "unstable" reading like from the O2 sensor.