Help - rough idle / engine pulsing

[Ranger X]

In short, my car is idling a lot rougher than I'd like. I don't remember it being this way when I first bought it. You can feel the idle in the wheel and seat, and it sort of "pulses", that is, it's rougher at times, in a steady interval. Also, if you open the hood and listen to the intake, you can hear it sucking or squirting something every once in a while, and feel the motor shake when it does it. (I have an SRI installed so it's easier to hear.) I'm sure it's related. This pulsing is also audible at times. What could be causing this? Dirty fuel injector or something? I'm also pretty sure I've got a bad O2 sensor on one side, could that be the cause? I'd rather not spend money to have it diagnosed unless I absolutely have to.

[totalreborn]

id do regular fluid change to mine...oil change...fuel injection cleaner...clean the throttle body..etc...

[Ranger X]

Yeah, I figure it could also be because I put seafoam in my crankcase right after changing my oil, and it's almost time for another change. The other day I used deep creep to clean the throttle body, but that didn't help much, since the intake is still just as dirty. I guess I'll wait until it's time for an oil change and see if that fixes the problem.