2AZ-FE Oil Pressure Problems

[chrisnstell]

I have a 2AZ-FE motor in my 2002 Tarago but I believe it is the same motor that his used in the Camrys.
A few days ago, the oil warning light came on whilst I was driving, followed by a noticeable valve lifter noise. I stopped the van and checked the oil which was down by about a litre.
I re-strated the car and the light went out and the noise was gone. I drove the car home and topped up the oil. I took the car for a drive of about 6 miles and the light came back on and again, a lifter noise. I nursed the car home and let it sit overnight, then started the car and had it running in my drive way for 40 minutes, the light stayed off until I drove the car onto the street. I don't think it is just a faulty oil light switch because of the accompanying lifter noise.

Today I removed the oil pan and inspected the oil pick-up. It had some flakes on it but they did not appear to be metal so I don't think they are from bearings.
There was no evidence of sludge in the oil pan or on the pick-up. I dont know the full service history of the car so it may have not been good before I bought it secondhand. It has done 140,000 kilometres.

Has anyone had a similar experience that may be able to shed light on what is happening?

[toyomoho]

Install an oil pressure gage. Oil pressure should be 4.3psi or more at idle, 36-78psi at 3K rpm. Could be a problem with the oil pump pressure bypass valve. Worn bearings will result in lower oil pressure. The oil light comes on at around 4psi. Have you recently been using a different brand/type of oil filter? Check for sludge by pulling off the valve cover.