Need help diagnosing vibration (1 Viewer)

[arcadian]

My 100 has intermittent vibration where the steering wheel oscillates back and forth, if I apply pressure either direction it lessens but does not go away. After it started I drove it to my mechanic and it was so bad I thought it might cause me to run off the road, speed was 15-20 mph was the fastest I could drive it. Mechanic said he drove it next day and couldn't find anything. I picked it up drove it for 30 minutes and nothing, drove 30 minutes next day and nothing. next day drove 2 miles to town and on way home it started again on way home. next day drove normal for about a mile then started. drove back to mechanic next day and was fine for about 5 miles then started. Mechanic drove it next day for about 20 miles then said it started some vibration, put it on rack and said he checked everything and could not determine the cause, said all driveshafts, u joints, cv axles, tie rods and ends, ball joints and control arms are good. this is an experienced former Toyota dealership mechanic that I have used for years and who maintains a lot of local Toyotas including mine for years. So I am at a loss, I defiantly have a major problem, anyone have any ideas?