cocogree

check engine light came on in 99 RX 300, gas mileage is horrible, 17 mpg on highway. Took it to Auto Zone, results showed BB System too lean - bank 1 probable cause BB1, lean air/fuel ratio fuel injector or vacuum BB leak, BB2 MAF sensor concern, BB3 ECT sensor fault, BB4 faulty HO2S
cleaned MAF sensor. Any suggestions?

Lexmex

Welcome to the Club,

What were the actual code numbers you got?

I suspect I see a P0171 already, but I'd need to know the specific numbers.

cocogree

My son took the car to Auto Zone and the print out he got only has what I listed in my original message. I was wondering about that as everyone else is mentioning codes starting with P0.

cocogree

If it's a po171, what needs to be done? I've been following other forums but am not sure what is being recommended. I see in a thread from 07 that you mention injector blockage.

Lexmex

P0171 by itself is likely something like a dirty MAF sensor or something temporary like climate-related issue. However, P0171 in conjunction with other codes doesn't carry that same weight. The codes are key because with different vehicles they can actually mean different things due to setups. In fact, Autozone should have given the Pxxx type codes as we've had others go there and receive them. There's no general recommendation we can give based on what you have.

cocogree

Ok, I took it back to Auto Zone and the code is P0171, no ther codes. MPG has dropped to 15 hwy.

Lexmex

P0171 could be the following:

-air intake hoses (check the ones by the airbox and the IACV valve)
-fuel line pressure/injector blockage (run some fuel injector cleaner through the system, Redline fuel system cleaner (Pep Boys has it) is the best stuff in my opinion in an all-around cleaner
-A/F sensors (doubtful), but sometimes as a result of a crack somewhere on the exhaust itself, either right off the manifold or underneath the engine), this doesn't necessarily mean something is bad with the sensor, just that it detected something out of whack.
-MAF sensor (needs to be cleaned)
-engine coolant temperature sensor (rare), because other codes P0115, P0116 would be involved
-exhaust system- as mentioned above by a/f sensors

One other one I might suggest now, but remote is take a look at your air filter to see how dirty it is.

cocogree

Thanks for your help! I go step by step trying everything you've suggested. My son did clean the MAF sensor though, admittedly didn't know what he was doing. We'll try that agian. If it needs to be replaced, can I get one anywhere (AutoZone) or does it need to come from dealer?

lexus114

Toyota dealer should have it,and it would be cheaper.

cocogree

Understandable that Toyota would be less expensive than from Lexus dealer. But what about saving about 80$ and getting one from AutoZone?

Lexmex

A strong piece of advice I have learned over the years about these vehicles. For things like this sensor or O2 sensors particularly, you want to stick with the original Denso brand. Unless AutoZone suddenly has the Denso brand, I'd stick to getting it as suggested through Toyota. A 2001-2003 MAF sensor for a Toyota Highlander V6 does the job, as it uses the 1MZFE engine as in the RX300. I should know, because that's where I got mine after I had issues with my own MAF sensor back in Dec. 2007.

code58

I couldn't agree more Lexmex, There are good aftermarket parts, but having spent my life in automotive work in one form or another I can say that seldom are aftermarket parts equal to original equipment Japanese (and possibly European) parts, if ever. We are used to using aftermarket parts on American cars because they come closer the quality of what those cars were built with. Not so with the Japanese, there are even Japanese aftermarket manufacturers that may equal the original equipment quality. Especially T/L, I would stick with OE.

cocogree

Thank you all for your suggestions! Replaced MAF and reset check engine light but it came back on. Went back to AutoZone for code and again, po171. I took the car to a reputable foreign car specialist and he replaced the o2 sensor and recommended replacing the spark plugs. The check engine light stayed off. I had the plugs replaced a few days later and that night the check engine light came back on, again P0171. The idle is back to normal and gas mileage has improved. Not sure what to do now.

Lexmex

This list should cover everything (as it also) includes what is noted in the service manual for this code):

This is the checklist for a P0171 code followed by my comments,

-air intake hoses (check the ones by the airbox (where the air filter is housed) and the IACV valve- for the IACV valve, see the DIY here, https://www.clublexus.com/forums/rx3...-write-up.html
-fuel line pressure/injector blockage (run some fuel injector cleaner through the system, Redline fuel system cleaner (Pep Boys has it) is the best stuff in my opinion in an all-around cleaner
-A/F sensors (doubtful), but sometimes as a result of a crack somewhere on the exhaust itself, either right off the manifold or underneath the engine), this doesn't necessarily mean something is bad with the sensor, just that it detected something out of whack.
-MAF sensor (needs to be cleaned)
-engine coolant temperature sensor (rare), because other codes P0115, P0116 would be involved
-exhaust system- as mentioned above by a/f sensors