hey,
i have the same problem just happend to me yesterday my oil pressure sometimes was really low and sometimes normal but my temperatures were all normal. I got a bit annoyed hoping it was nothing to do with my oil pump so i checked the oil levels and discovered it was running dangerously low. I couldnt think of were all that oil went as i checked it all a week before and then i remebered when of my coil packs went on me and the car was on 5cylinders for a couple days while i was trying to find a coil pack from wreckers. I discovered that running on the 5 has burnt a lot of oil out and its really dirty when i checked it last night this morning i am heading to go buy some new oil and a complete oil flush i will tell you if that has cured my oil pressure problems.,
Also sorry for the long reply (noob to forums)