1995 2.2l Manual tranny trouble with CO

So I took the car in to get emissions and the thing failed, bad. It had twice the normal CO level.

Ocassionally when driving down the highway it will toss a CEL and stutter(not always at the same time). It usually does this at cruising speed and giving it gas clears it up. It idles fine, starts fine, has great power under load. In stop and go traffic i have no issues whatsoever.

I pulled the codes(I hate the inbetween bastard obdII setup BTW).

first threw a 55 - Lean Fuel monitor error and shortly after threw a 13 - O2 sensor error

The O2 is new
The plugs are new
the filter is new

Any ideas?

The code 55 is a pcm or pcm prom problem.
The code 13 is a 02 sensor circuit or o2 sensor.
Check wiring and plug in. also check wiring at pcm also could be a bad PCM.
Check the prom and make sure it is pluged in good and clear codes and recheck.
Is the check engine light working?
MT-2500

I hate PCMs.

The O2 is brand new and the issue was the same before replacing it.

The CEL(check engine light) works just fine. It sometimes comes on during the above mentioned situations

Where is the PCM on this car anyway? I haven't really looked at it yet. Picked this car up as a commuter 6 months ago and replaced the clutch, after that fun I haven't really peeked under there.

Behind right side of front fascia on impact bar.
Right front corner of car.
I think some of them had a tsb on water getting into the PCM.
On the 02 sensor code a 02 sensor code does not say replace the sensor it says check it out. It can also be the wiring circuit or even the PCM.
With the code 55 it is time to look for that PCM.
MT

he's right, a O2 sensor code doesn't mean the sensor is bad, it just gives you an idea of where to look. After finding an O2 code, i replaced my O2 sensor twice, only to find a burnt wire. Also, check the individual wires and plugs going to the fuel injectors for chaffing/burns. A misfiring injector will throw a lean code.