2004 Dodge Neon SXT - rough idle

Few times last year, when I start my engine, it would feel as if the engine is trying to catch but wouldn't crank. When this happens, I would press the gas pedal to rev it up a bit, and the engine would catch on and crank up. It happened maybe once or twice a month for the last year. It stopped doing that and starts up normal now (didn't do anything to it). Engine light would come on sometimes, computer says fuel line has possible leak. Whenever it came up, I would tighten the gas cap and reset the computer (I use locking cap). It seems to work and has not came back on for a year.

Last month, my car started to idle pretty rough. It would shudder when I stop the car at intersections, but it would drive smoothly over 30 mph. The RPM does not move up or down while idling though. It stays at around 900 RPM. I changed all of the spark plugs and wires. I did notice a little oil around the fourth spark plug, but it was not in the engine because there was no oil on the threads. The idling did not improve after changing the plugs/wires.

My car is at 152,000 miles right now. Manual trans. Replaced clutch at 120k miles, flushed out coolant, replaced radiator cap/thermostat and spark plugs/wires at 150k miles.

Any idea why it is idling rough? Could it be bad fuel system? If so, what should I do? Replace the pump, clean injector, what??