Why is my car running rough?

I have a 1994 4clynder Toyota Camry that is running
rough. Mostly on idle. It tends to be fine when it's a a bit
higher of a rev point. When I first noticed the problem I
checked my spark plugs and found a bit of oil in a couple
of them. Had the oil issue fixed. I also noticed that they
were pretty worn, so I replaced the spark plugs to. I also
ended up replacing the wires, distributor cap, and rotor. It
didn't change anything. While I was at work my fiance
cleaned the throttle body and the issue almost entirely
went away, and we threw in some fuel system cleaner to
see if the occasional rumble that was left was just gunk in
the system. However the issue started getting worse
again. I found out that he didn't replace a gasket that he
took off and I plan on doing so asap, but if that doesn't
work what next? It tends to be okay when I'm at a stop and
throw it in neutral and have it rev at 1.5 thousand rpms.
Also probably unrelated but it just had an oil change so
that's fine. And I have been keeping an eye on the coolant
which is also doing fine