Is the shaking only in the steering wheel, or is it simply more pronounced in the steering wheel than anywhere else? High speed shaking is 99.9% tire/alignment problems.
Where does the shaking seem to originate from? Driver’s side rear, driver’s side front, passenger side rear, passenger side front, or is it car-wide? What speeds does it appear/disappear at? Is it RPM specific? What weather is it worse/better in?
My suggestion is to take it to a REAL mechanic, even Satan (the dealership) and take the mechanic for a short ride so he can experience the problem himself. If you’d rather not spend the money (and you should, it’s your safety we’re talking about) then you can go down this checklist to eliminate or specify the problems.
1: With the car parked and cold, check to see if the lugs are tight enough. Grab the wheel and shake as hard as you can, front to back and side to side. It should not move seperately from the vehicle. If it does move without shaking the vehicle as a whole, your hubs are probably bad. This is unlikely, but the easiest to check and so number 1.
2: Go to a real tire and brakes garage and have them re-mount and balance the wheels and tires. This is almost positively your problem.
3: Go to a real alignment shop (probably the same place) and get a computer controlled alignment.
4: Check the boots on your CV joints for grease leaks. You will have four joints, driver’s inner and outer and passenger’s inner and outer. Drive the car around a sharp turn slowly with your window down and radio off and listen for a creaking, ticking, tapping, or thumping noise that only appears during a turn. Go both right and left to check both sides.
5: Go to a frame shop that does computer controlled frame straightening and have them check your frame.
6: Find someone weighing approx. 200 lbs. Have them sit or stand on your bumper/hood and jump off. Also have them push down on the vehicle’s fenders as hard as they can and let off. Your vehicle should quickly raise itself level without bouncing. If it bounces or otherwise seems loose, your suspension probably needs replacing.
These go from basically free to rather expensive, and from probably it to not likely. Go down the list one by one, and you may stop when the problem disappears.
One final word of advice: Do not ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever, ever go to Wal-Mart, Sam’s Club, K-Mart, Target, or the like to get your vehicle serviced. NOT EVER. Do not EVER go to Pep Boy’s either. If you don’t think I know what I’m talking about, ask around the board. They’ll tell you to listen to me. DO NOT GO TO THESE PLACES! They are cheap, yes, but they are cheap! Your tires, and car as a whole, are responsible for your safety, and in some situations, your life. Saving $10 on tires is NOT WORTH IT!
Please don’t think I’m trying to be a jerk about this, but I cannot impress upon you enough, or anyone else, how important it is to NOT visit these sorts of places when your vehicle needs maintenance. These places generally do not care about you, your vehicle, or your safety. They are paid minimum wage and are unskilled. They have been taught how to take a wheel off, put it on the machine, and let the machine do the rest. I’m sure there are some very good mechanics working for them, but - strike that - if they were good, they’d be working elsewhere.
Some places that I have found are somewhat knowledgeable and reputable are NTB (National Tire and Battery) and Tires Plus+. Almost certainly the best place to get your vehicle worked on, however, would be a local Toyota dealership, but you will pay a premium.
Good luck fixing the problem!
–Tim