Ask the dealer about Engine Sludge and ask them to do a check for it. Other signs of sludge are smoke in the exhaust on first start up, high use of oil -- greater than 1 qt. per 1000 miles, and thick oil on the dipstick. Even if you just have light coming on, Toyota is supposed to do a free check for sludge. Call their sludge hotline. You can find the nubmer at
http://www.autosafety.org