'86 560sel low oil pressure, idles rough

[dvdguy]

I just picked up an 86 560sel with 100k miles. The car has a bit of a burble when idling- almost as though it's missing, and the whole car shakes a bit. The car idles at 5-700 rpm. At higher rpm (over 1k), the burble seems to go away. the engine feels strong, the trans. shifts smoothly. I have not driven the car much as of yet.

I just noticed that the oil pressure is low. It idles at under 1 bar, and pushing the accelerator will bump it a tiny bit, but it still hovers below 1.

Oil levels look good.

Do I need a new oil pump? how much of a job is it to install one? I've done a few simple things like water pumps, etc, but never an oil pump in a Benz.

anything else I ought to look for on the 560? I assume that doing the timing chain would be pretty easy once things are apart and 100k it's about due for one, yes?

thanks!!