Toyota's use shims to adjust the valves and you must use a special tool set to compress the spring and remove the shim. You would want to measure valve clearence on each valve on a cold engine and compare to factory specs. I would also have the cam bearing caps checked and cam wear in general (bearing surface and lobes).
As far as the oil you are either burning it or leaking it. Although it may not be visable, if it is not leaking it, is burning it.
Have a compression test performed on the engine.
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Friday, October 17th, 2008 AT 8:00 AM