legacycentral bbs

so my car just turned 250k!!!! but anyways it has ben idling very low at about 400rpm and shakes the whole car for about a month now and just last friday it started to almost spudder mainly in first gear. was hoping it was just the spark plugs, i changed them out and so far the spudder has stopped but when its warm and i drive it for a while then come to a stop it idles just fine, then about 15 seconds it starts to drop down to about 500 and shaking again.
In one of the cylinders when i was changing the plugs there was quite a bit of oil and gas on the spark plug, whats this mean and how bad is it?

could that be the cause of the low idle? what should be my next step, fuel filter, pcv valve, wires?

any advice would help!?

I'd suggest doing the spark plug wires next. What other "routine maintenance" stuff have you done recently on the car?

recently not much other then oil changes

The oil & fuel on the plugs is an indicator of poor/incomplete combustion. This can be caused by several things, but it's usually ignition related, which is why I suggested to do the plug wires.

valve cover gasket, change the plugs and wires as well