98LS?

I have been through quite a few similar threads and am leaning towards 02 sensors at this point but, wanted to get some other opinions along my way. 98 coupe 80,000 axle back exhaust and thats about it as far as i know. Bought her the first week of June. So a few weeks after I got it i had freak misfire. Engine shaking heavily,bad exhaust smell w/ smoke under acceleration. lasted maybe ten minutes in driveway then cleared up. p0300. Now three months later starting friday it picks and chooses when it decides to run good or extremely rough like that one time it happened. always only p0300 if it codes. new a/c delco plugs and wires. all fuel trims show between -5 to -95% at most times during its episodes. Just really strange for me to think its fine this half a dozen times,episodes once then fine again. Connections good at 02's,maf,iat,map,pcm.etc. Thanks in advance for the help!!