Let's get ready to rumble

[Kent McLean]

Or in this case, stumble.

On my last trip from NC to NH (about 850 miles, for
those who are curious), my car was running great on
the backroads of NC.  I stopped to get gas at a Citgo
station at a fairly busy intersection in a fairly big town
(Washington).  I hadn't gotten 100 yards down the road
when my car started to hesitate and stumble, like it had
water in the gas.  It ran fine on the highway but hesitated
and lacked power getting up to speed. And my gas
mileage tumbled (down to 18 mpg from 21 mgp; a full
tank usually shows 450 miles to empty; now it would
show 320). Two tank refills later in NH, I put in some
 dry gas and  Techron.  Things got better, and I
was heartened to see 21 mpg and 420 miles to empty.
But after 5 tanks of gas and some more dry gas
(isopropyl alcohol), there was still a slight hesitation, a
very slight stumble.

Time to pull the ECU codes [1]. I went to Radio Shack
and found an LED with resistor for about $US 2.00.
After some trial and error, I got it to flash out 234.  But
as it was my first time pulling the codes, and I wasn't
sure about the 3 digit code, I pulled fuse 21 to reset
the ECU error codes, and took it for a fun ride: back
roads, third gear, blasts to 70, and 1.4 bar.  God, I love
my 200.

Back at the ranch, I tried pulling the codes again -- 4444
(ECU is happy).  Dang.

So the question to the collective is, "What next?"  Any
ideas of what to test, clean, or replace?  Do y'all think
the "234" could have been a "2342" bad O2 sensor?

Thanks,
Kent in NC
'89 200 TQ, "Night Train"

[1] http://www.sjmautotechnik.com/ecuf_MC2.html
    Thanks Scott.