Ive got a 1990 2 door montero that has really low oil pressure when idling after being fully warmed up almost to 0lbs. When driving however it it will bump up to around 30lbs. Anyone have any ideas? I was thinking maybe the oil pump but I was just wanting to make sure before i replace it.

 

its normal... the faster the engine, the greater the pressure

 

When was your last oil change? If the oil is contaminated, and thins as a result, this could be the issue. Starting with an oil change might not be a bad idea. If the problem continues, I'd then check to make sure the gauge is giving you a correct reading and working properly.
Next, check the wiring. Have someone sit and monitor the gauge while you move the wiring from the sending unit. If the gauge "bounces around" it's mostly likely the wiring.
If both of those items aren't the problem, the pick up line could be clogged, or the screen on the pick up could also be clogged. Oil pumps are the only part of the system that run on unfiltered oil, so check the parts that feed the pump first. Finally, if nothing else helps you find the problem, replace the pump itself. It's the most expensive repair in the series, so I'd check everything else first.
Good Luck