poor fuel economy, idle surging, and more!

[nde264 at lulu.it.northwestern.edu]

Lately, I have been having what could be described as a cold start problem with
my 89 90q.  After the car has sat for over 4 or 5 hours, when starting, the
engine starts, drops to 500 or so rpm, surges to 1200, then settles down to
around 1000.  For the next minute or so, there is definite hesitation upon
acceleration until the engine warms up a little.  Rev through 1st gear, shift
into second, hesitates at 3000-4000 rpm.  Also, depressing the clutch going
into second gear, the engine speed seems to back off very quickly, sometimes
causing the car to buck.

After the engine has "warmed up" (the coolant temp gauge isn't coming out of
the first set of closely spaced tick marks, though it was at the middle of the
range this summer), it idles at somewhere between 1000 and 1300 rpm, usually at
around 1200.  When driving for over a minute or so at about 45 mph in 4th and
coming to a stop light, when I depress the clutch and roll to the light, the
idle drops to 1000 or so, then surges to 1600-1800 rpm for about a second, then
drops back down to 1200.  There don't appear to be surges under acceleration
once the engine is warm.

All the while through these problems my car has been getting BAD fuel economy,
between 13-15 mpg city, but 25 or so highway.  When I first bought the car it
was around 22 city, 29 highway.

Pulling codes results in 4444.

I am thinking that this problem can be either one of two things, O2 sensor or
multifunction temp switch?

I replaced the O2 sensor in April, but at idle the voltage reads around 60-100
mV, not the .5V I expect.  Revving the engine while measuring voltage results
in a voltage rise concurrent with engine speed up to 1V at 4500 or so rpm, I
have not gone higher yet.

TIA,

Nathan Engelbert
89 90q