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?