my 2006 sienna running lean both banks

P0171 TOYOTA - Air/Fuel Mixture System Lean Bank 1.... Possible causes - Intake air leaks - Faulty front heated oxygen sensor - Ignition misfiring - Faulty fuel injectors - Exhaust gas leaks - Incorrect fuel pressure - Lack of fuel - Faulty Mass Air Flow (MAF) sensor - Incorrect Positive Crankcase Ventilation (PCV) hose connection.... If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced............................ P0174 TOYOTA - Air/Fuel Mixture System Too Lean Bank 2.... Possible causes - Intake air leaks - Faulty front heated oxygen sensor - Ignition misfiring - Faulty fuel injectors - Exhaust gas leaks - Incorrect fuel pressure - Lack of fuel - Faulty Mass Air Flow (MAF) sensor - Incorrect Positive Crankcase Ventilation (PCV) hose connection..... If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced.

I replaced all o2 sensors, maf sensor to. The only part I Haven't replaced is the pcv valve. I also did a smoke test the only place I seen smoke is from the air filter assembly its missing a fastener and it doesn't seal properly. Can this cause the lean code. I erased the code, drive the van for about a week and the code comes back on.

We had same problem car came back from dealer service with check engine lights and hesitation at initial acceleration, (P0171 & P0174). We replaced all O2 Sensors. No help. Turns out that the dealer "Toyota of Tampa Bay" left the air intake box loose with missing fasteners. They left main intake plenum hose loose, the MAF connector smashed and a vac line disconnected. All this presumably from when they opened up the air box to sell us a $50 air filter. This type of behavior has been consistent from this company. Be careful who you let work on your car. Check these items: Air Box, Plenum, vac lines and PCV before you start replacing sensors like O2 & MAF.

thank you.

update on my sienna.. I did a smoke test and notice smoke coming from the air tube hose connecting to the throttle body, the clamp was loose my mechanic left it loose. I remove the air filter housing and checked the hoses for cracks, clean the filter box install a new air filter. put everything back together make sure the hose clamps were tight, install the fastener that was missing on the air filter box.. I drove the van more than 300 miles, checked it with the scanner and all emission are green light , no more codes.. I want to thank everyone that responded to my car problem.