My newly bought (2 weeks ago) 2010 Lexus RX350 w/140k miles has P0171/P0174 system lean codes. My long term fuel trim is typically 15-20% (w/STFT between +/- 4%) and I only get 14-16mpg with conservative driving. I've already cleaned the throttle body & MAF sensor, so I'm assuming it's a vacuum line but want to make sure I'm going in the right direction. How should I go about diagnosing and fixing this?
https://www.youtube.com/watch?v=zMok2y05jNE
I usually just spray cleaner around the intake and listen for RPM increase.
Plenty of youtubes on how to check for vacuum leaks. It's pretty generic stuff, but on yours don't forget to inspect the air intake valve. You'll see a vacuum line going to the unit BUT don't stop there.
The unit has a shaft which runs from the outside of the intake manifold to the inside and it gets worn and leaks.
Often it only leaks in one position so you want to grab where the vacuum control linkage attaches to the shaft and apply lateral pressure while spraying carb cleaner/starting fluid on the shaft and listening for changes in idle or watching for changes in fuel trims
Part #17320 0n the diagram:
