Hey scotty big fan!
I recently bought a 2009 lexus is250 that has 130k miles.
I changed the oil to synthetic, the pcv valve, spark plugs, and the intake manifold gaskets and I have burning through oil like crazy. It's not leaking under the car or anything from what i can see so I suspect it's burning since I've had to add 3 quarts in almost a month and a half. What could possibly be the issue? Car runs great except for an occasional dip from 700 rpm to 500 rpm but other than that it's been good. Thank you for the help.
It's either burning or leaking. Were the old spark plugs oil fouled? Is there oily residue in the tailpipe?
The engine could be worn due to lack of maintenance, but you might want to double-check for leaks using UV dye.
https://www.youtube.com/watch?v=LYzTyTlnsr8
I checked the tailpipe it has black soot in it so not sure if that's oily or not. Previous owner said he did syntethic oil changes religiously. Yes some of the previous spark plugs were oil fouled. I'm scheduled for a mechanic next week so I guess we will.
Unfortunately all signs point to oil burning. When buying a car you can't believe anything the seller tells you, a thorough pre-purchase inspection by a good mechanic is needed.