How's your coolant levels looking? White smoke's normally coolant. Not sure I'd usually describe the smell as "burning", but it kind of depends on the antifreeze being used. I'd also tend to believe that the head gasket is on-and-off leaky rather than the stem seals leaking so much that smoke is "billowing".
Um, valve stem seals will cause blue smoke....
White smoke is the Head Gasket from coolant.
Also leaky valve stem seals will usually just show a puff of bluish smoke at cold startup after the engine has been sitting a while. If the valve stems are leaking that much and you are blowing smoke while driving, you should be burning a LOT of oil. How much do you burn? Valve stem seals can be replaced without removing the heads if the correct tool is used. There is such a tool out there. Not sure if the dealers use it. I doubt it, but maybe. I assume this is an I4 based on the quotes you are getting.
I agree with the others. This is likely a bad head gasket.
Exactly my sentiments. From what I had gathered, white smoke is a sign of anti-freeze/coolant getting leaked into the combustion chamber which, in turn, is an indication of something being wrong with the head gasket.
However, the oil dipstick does "not" show any sign of antifreeze contaminated with the oil as I do not see any "milky" mix. But at the same time, the white/grayish smoke that came out of the exhaust pipe, that one time, had a bittersweet/burning gas odor. But I am sure it wasn't blue smoke so I have no idea why the Toyota dealership had a diagnosis that implies the smoke was blue.
A few other points, the oil and coolant levels are both above full -- oil perhaps a bit too much. Could it be because of higher level of anti-freeze and oil, these problems are starting to show up? I only changed the engine oil and added coolant 3 weeks ago and the last week, I had a misfortune of watching my car blowing a huge amount of white/grayish smoke. The smoke so far occurred only once if that's any consolation and I've been driving the car for the last 4 days with no smoke.
If it is indeed a blown or leaky head gasket, why did it only happened once -- although I had driven the car that day for over 40 miles when it start emitting smoke as opposed for the last couple of days that the car has been driven for around 10 miles for any given trip. Could the valve seals be the culprit after all? How much does a head gasket for a 4cyln cost, $100-$150? The car also has 90k millage.