GOOD LORD. let me clear up this oil consumption issue. 1-2 quarts of oil in 5k is NORMAL. oil consumption happens because of looser ring tension. this helps with fuel mileage, power, and engine life. a by product is blow-by, which causes oil consumption. IT'S NORMAL. and i bet no service advisor in my "Elite" "mega" dealership knows that. WHY??? because the oil light won't come on until you loose almost 3 quarts. so customer's don't know. most techs don't check oil before they change it. so how would you know???? the germans know because they have electronic oil level gauges that tell them the exact level and warn them when only 1 quart is low. official limit is 1 quart per 1200 miles. but if you are burning more than 2.5 quarts per 5k, that's probably indicative of a problem. you're right on that line. it's suspicious.

NOW ABOUT YOUR problem. you may have a head issue. there is a service bulletin for it. too much clearance in the valve stems causes a slight knock that can be picked up by the knock sensors. this retards engine timing and "knock correct learned value". this can get so bad that the car may not even go faster that 30 mph. guess what else is a by product of this problem......oil consumption. there has been a service bulletin out on this issue since 2008.

your warranty may be 100,000 miles, but it will still be 6 years from date of first use. be careful of that. also, after 70k the warranty isn't factory, it's lexus extra care.