Help with 96 3.8

The 4 digit code was what exactly?
There is no code for a bad you must mean O2 sensor (there is no carbon monoxide sensor)
Sounds like your car has a misfire hopefully not a dead hole
P0172 and P0174 Means You need to check the intake gaskets check the fuel pump pressure then possibly replace the HEGO's
Pinpoint test steps are needed possibly with a 105 pin breakout box. That gets ugly.
There are a few shortcuts if you have access to a NGS or pid reading scan tool
Yes it could be the ECM but uncommon on sequential like your '96
Check every injector with a noid light
Find a scan tool you can borrow and check the long and short fuel trim pids
Check all the HEGO pids Watch them switch (cycle) above and below .5volt quickly. They run in stereo and need to switch at the same rate or you get the CEL on
Report back

Great thing about 3.8's
They do not blow up
They do not burn oil
They do however burn valves
Transverse engine applications eat head gaskets
WynnPaul shoot compressed air into all 6 spark plug holes using a good compression tester
Check for air out the exhaust pipe or intake manifold see how much comes out the oil fill
The pistons need to be at or near TDC on their firing stroke with the valves closed for this test
Common for the rear two cylinders to burn exhaust valves on 3.8