Erratic idle and RPM's, terrible fuel efficiency and surging

It started a few months ago with a rough idle at stop lights. I replaced spark plugs which helped for a day or so but it came back. I read about broken ignition coil or fuel injector wires being a common issue so I checked that out. There were two that were suspect looking so I spliced them and put dielectric grease on the connection terminals. Same thing. Drove amazing for about a day and then went back to the same problem again. Idle is becoming worse and more consistent. Replaced air filter and clean MAF sensor. Gonna clean throttle soon. Not sure if it being dirty can cause such severe issues. Sometimes (usually at lower speeds, about forty mph or so and below but sometimes at highway speeds) it will surge or damn near stall while driving. AC makes it worse but that is just due to the extra load (I think?).

Some extra information that could be me being paranoid:

No CEL(check engine light). Car turned over real hard one morning and locked up. Had to try three times before it got it. CEL came on then went out.

Sometimes smell gas but can never smell it in engine bay.

Noticed that instant mpg is real erratic. It will jump from about eighty to twenty or thirty with no change in speed. Like I said though, not sure if this is normal.

I am thinking it is a vacuum leak? Already tried the break boosters and those are fine. Engine temperature holds steady a little under half. Maybe a clogged cat? As with any of this being from a bad sensor, wouldn't that cause a CEL? I am at wits end at this point. It could be so many things and they all have basically the same symptoms. Any help is greatly appreciated.