you need to monitor the oil pressure with a replacement direct reading mechanical gage with a 1/4 inside diameter steel braided teflon line.
the stock gage is verrrrrry inaccurate.

if the idle pressure is below 20 I would shut it off and not run untill it is fixed...!!!!

 

a good rule of thumb is 10psi for each 1000 RPM is sufficient. sounds like you're in that range, but it's definately lower than i would like.

 

Just like Kato said, use a good mechanical gauge so you know where the oil pressure is actually at.