2002 Avalon with P0171 &P0174 codes

[gliras1]

I have a 2002 Avalon with a check engine light on with the codes P0171 and P0174. We have already replaced both oxygen sensors before and after the cat. Cleared the codes and test drove the car, light did not come right back on until we drove it for a while. Anybody have any suggestions? Someone said to either clean or replace the MAF? Could this fix the problem? I need help here? Thanks

[fraw]

The best & wisest thing to be done here first is, try cleaning your MAF first dude. If it didn't work then that's the time you go for plan B.
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[cking35@bellsouth.ne]

I have a 2000 avalon, about 9 months ago the check eng light came on. I have a code reader and it had codes po171 and po174, left bank lean. I have cleaned the MAF, removed the left oxy sensor, looked at it and re-installled, but did clean the connector. The light continues (CEL) coming and I contiue to erase it. The best cost for a oxy sensor I have found is $154.

[Eurobob]

cleaning my maf didn't do anything. still had the same codes. i replaced the sensor altogether and it worked like new

[new echo owner]

Interesting, just keep throwing parts at it until something happens.

N.E.O.

[2MCHPWR]

i have 2002 avalon and got the P0171 code.
it says bank 1 lean.
which is bank one? closest to firewall? I cleaned mass air flow meter already.
I want to swap the O2 sensors to see if the code changes as well. then i'll know if its really a bad o2 sensor. right?

[new echo owner]

A 2002 Avalon would have A/F sensors for sensor 1. Bank 1 is always the bank where #1 cylinder is located on, in this case it is the rear bank. MAF would have affected both banks, since it is only bank 1, it is very likely that you will need to replace the A/F sensor, which is on the exhaust manifold before the cat. Swaping the A/F sensors is one way of testing it, but there is also the posibility of the sensor sieze in the manifold when you do that.

N.E.O.

[Eurobob]

if it is lean, you may have an injector stuck static closed on that bank. i would replace the sensor and see if it goes away, if it doesn't return it. does the car idle or run poorly? if the answer is no, i would still say that the maf sensor is bad. the pcv is on bank one on the passenger side, but i don't see that causing the problem that you have. Lean is you are not having enough gas and the fuel trim can not correct that much of a problem. if an injector is stuck closed, you can put a small wrench on the injectors and slightly tap them with a hammer. if something is blocking it, that usually clears it out. that bank is a bitch to get to though. i just don't see an o2 sensor going bad unless you run way too rich and dump raw fuel on it or you are running leaded gas which is almost impossible to get a hold of. toyotas have a lot of blow back from the crankcase line and the oil gunks that sensor up to the point you can not clean it. it is a delicate sensor too and may get damaged trying to clean it in the first place.

[NEZ]

If your getting both codes P0171 and P0174 its either the MAF part#22204-07010 or you have a hose either loose or backwards your vacuum switching valve located on the air box. If your VSV is bad the part# is 90910-12199.