I have a 2001 ES300 with 166,000miles on it. Never used a drop of oil but I've had to add 3 qts in the last 1000 or so miles. Thought I saw a puff of blue smoke on start up once last week. Have also had a little ping at low speeds lately but premium gas seems to help that. Temp is normal, no smells or leaks. Could this be the start of the dreaded sludging?