low boost? CO ratio?

[Benjamin Weste Pearre]

Another question (1990 200TQA) -

I moved from sea level to Boulder, CO, and found that I was getting
about 33 MPG on the highway, but that my car would stall whenever the
engine went from high-ish RPM to idle, especially before it warmed up.
A mechanic here found that my CO mixture was low - 0.12 - and adjusted
it to 0.8.  This brought my mileage back down, but it fixed the
problem.

Or did it?

I'm not exactly sure what he did, and my car subsequently passed
Colorado's emissions test (on the 4-wheel dynos they use here!), but
surely the ratio being so far off indicates a bad sensor.  Which one?

I should mention that when my car is warmed up and I floor it,
sometimes I get 1.4 on the boost gauge, and sometimes less (1.1,
1.2, and less acceleration).  There's an intermittent fault
somewhere - does that mean I just have to replace every possible
culprit?  Who are the usual suspects?

My throttle switch behaves sort of right: about 0.1 ohm in the right
place on the idle switch, but the WOT switch, while adjusted
correctly, seems to be about 1.6 ohms (sounds a little high?  Does
this matter?).  It was replaced (repaired?) before I owned the car, at
about 112k miles (now I have 178k).  Should I just replace it to be
sure it's not guilty?  It's easy to get at, at least, though I don't
know what it costs.  Moreover, it shouldn't be able to affect the CO
mixture!

If I want to upgrade my ECU (with, say, the Force 5 mod, etc), are
there any other things I should watch out for?  Should I have a
mechanic do a vacuum test everywhere?

Thanks!
-Ben

--
Ben Pearre          1990 200TQA          http://hebb.mit.edu/~ben