96' s500 stalls at idle intermitant

[mtl-s500]

i resently bought my benz,the engine runs great, the problem happens when I'm at idle, the idle jerks or the car just stalls,but it starts up great,when I accelerate the engine will cut of for a fraction on a second.
I've notticed that when it is in "stalling mode", at idle the oil pressure is under or at #1, there is no light that come on when it stalls,their is one time that the batterie light flickered when at a stop and the rpm jerked and whent below 400 and snaped back to 2000 before going back to idle, wich is about 650 rpm .At first it would only happen once a week but now it seems to be doing it every other day.I dont have the history of the car, this week I will do a good tune-up (plugs,wires,etc..).

thanks for the help!