I got a 94 Astro Van that seems to run fine when you are driving ,but when you stop at lights or stop signs she will shake pretty badly and the oil pressure will drop all the way down with the gauge bouncing up and down. When I hit the gas again the oil pressure jumps back up to about the midway point on the gauge which I would figure to be about normal. Any clues what is causing this and where I need to be looking first, I thought maybe it was low on oil but when I check the oil she seems to be within range. Thanks for the help.

I got a 94 Astro Van that seems to run fine when you are driving ,but when you stop at lights or stop signs she will shake pretty badly and the oil pressure will drop all the way down with the gauge bouncing up and down. When I hit the gas again the oil pressure jumps back up to about the midway point on the gauge which I would figure to be about normal. Any clues what is causing this and where I need to be looking first, I thought maybe it was low on oil but when I check the oil she seems to be within range. Thanks for the help.
It sounds like the idle is dropping too low and resulting in low oil pressure.
Try cleaning the Idle Air Control (IAC) valve and see if that restores the idle.
If it doesn't allow normal idle, it may require replacement.