failed emisions

I recently failed the emisions test. its an 88' ranger 2.9
my hc was about 18. and co passed but was high about 33
I did a complete tune up before the test (cap, roter, plugs, wires and
fuel filter)
I replaced the o2 sensor after the test and the exhaust smells better
now not just
pure gas. but the idle is still surging a few hundred rpm ans has some
hessitation.
Need some advice could this be egr or maf or map?