I have been trying to fix a lean issue on both bank 1 and bank 2 on my 2001 Lexus IS300 for several months now. The car has a lot of mileage, 358K miles. I have owned the car nearly 10 years. I always change the oil every 5K miles with Mobile 1 5w-30 synthetic oil. I clean out the throttle body every time before changing the oil and with a new Wix oil filter. I replace the air filter every 15K miles. A few months ago I received a check engine light. I plugged in my scanner. I ran diagnostics and it says that I have a P0171 code "System Too Lean Bank 1" and P0174 code "System Too Lean Bank 2" with a exclamation mark for both codes. After replacing the MAF sensor with a new Denso MAF sensor, I now only have an exclamation mark on P0171 code and pending for P0174 code. I was told by two mechanics to replace the fuel injectors. So I had that done by a mechanic. with new Denso fuel injectors. Also, all brittle hoses and the PCV valve were replaced. Yet, I still have a check engine light with a exclamation mark on code P0171 and is still pending for code P0174. I have no idea what I should try replacing next. Maybe a smoke test to see if there is a vacuum leak somewhere. Also, I did replace the VVT solenoid at 258K miles. Any ideas what could be the culprit?

 

171 & 174 are codes or a vacuum leak.