Does the oil pressure warning light work? The Montero doesn't have a 'real' oil pressure gauge. I was getting low (<10psi) readings on mine. I replaced the sender unit with a generic unit and it reads within the normal range now. It's really, really easy job to do when changing the oil. If you really did have 0psi oil pressure at idle your HLAs (lifters) would be clattering like crazy. I plan on getting a real gauge in the future. Anyhow, if your pressure is still a little low try a Mitsu filter if you don't use them already. If it's STILL low, you've probably got a weak pump.

Good luck. <img src="/forums/images/graemlins/kewl.gif" alt="" />