2009 RX350
Trouble code P0171&P0174

I used another vehicle(toyota sienna)'s mass air flow sensor to replace my car's mass air flow sensor, but it did not work. Through the similar method, I replaced the oxygen sensor, B1S1 & B2S1, but it did not work either. And no air leak was found after I checked. The long FT was still high. I have no idea about the problem.

the trouble code:



700 rpm mass air flow:


700 rpm short FT & long FT:


1800 rpm mass air flow:


1800 rpm short FT & long FT:

 

2009 RX350

trouble code P0171&P0174

I used another vehicle's mass air flow sensor to replace my car's mass air flow sensor. And through a similar method, I replace the B1S1&B2S1. but the long FT was still high. I have no idea about the problem.

trouble code:


700 rpm mass air flow:

700 rpm mass air flow

700 rpm short FT & long FT:

700 rpm short FT & long FT


1800 rpm mass air flow:

1800 rpm mass air flow



1800 rpm short FT & long FT:

1800 rpm short FT & long FT

 

Another new member!
Welcome to Club Lexus.

If I remember correctly my new MAF sensor was putting out 3.3gm/s.
Your MAF may be damaged.

Looking at your fuel trums at idle at approx 50% for each bank is very high and suggests a tear in the rubber air tubes on the throttle body drawing massive unmetered air.
Recommend pulling both rubber tubes and inspecting for cracks or not being installed properly.
If the leak is not found here, can look around because it's sucking ar somewhere.

Also noticed your fuel trims improved to approx 35% for each bank with raised idle and this is again confirmation of a massive vacuum leak.
I think you have 2 problems, massive vacuum leak and bad MAF sensor.

 

I had to buy the Denso MAF, the first aftermarket one I tried kept giving me the same codes 171/174. No problems after getting the Denso. It’s only a little bit more expensive but worth it.

 

I feel your pain. lol
My fake Denso on I bought on ebay for cheap did me the same way.
PS- I'd check for vacuum leaks first since this can make the MAF report low numbers if it's sucking air from somewhere else instead of thru the MAF sensor.

 

Yes, vacuum leak would be first logical assumption.
Visual inspection for broken fittings on and near air filter housing. I broke one of mine when I changed the air filter -- they snap off easily.
Smoke machine would be handy in this case.

 

I replaced the MAF sensor with another sensor which is Denso brand from a Toyota sienna vehicle, but it did not work. And I replace the air filter housing, but it did not work either. Maybe I should check the intake manifold if there is air leakage.

 

thank you for your suggestion

 

Thank you for your reply. The leakage is really hard to find. Do you mean a smoke machine leak detector?

 

Shown below is where mine was leaking but there are more places to leak, plz see posts above and hopefully others have ideas too.
Guping lots of "unmetered air" from damaged rubber tubes causing very big vacuum leak and it was raising my fuel trims very high and throwing lean codes.

Took these today to show.

 

Thank you so much. I have no tools to handle this. So I have to go to the auto repair shop to do this. And I have made an appointment first. I will release the latest progress after I go to the auto repair shop.

 

I went to the repair shop. The chief unpacked the throttle valve and then install it. The problem still exists. The chief tested the fuel pump pressure and it indicated the pressure is normal. The pictures are shown as follows.




The chief has no idea about the problem. He suggested I find a Lexus dealer to make an appointment to conduct a professional check and get the report.

 

I like to thank you for courtesy update.
It's so nice when members are courteous and reply when people try to help.
You said a lot so plz let me break it up.

From your pic, your engine has excellent mechanical vacuum at the manifold.
This means you can rule out compression, bad valve, leaking manifold or manifold gasket in my opinion.

Excellent, this rules out elevated fuel trims and throwing lean codes due to low fuel pressure.
This happens a lot but you are ok here.

Someone will have to dig in deeper.
Your fuel trims are elevated and your MAF sensor is reporting low numbers and it improves a little at raised idle.
This is classic for a vacuum leak after the MAF sensor but before the manifold.

Can also be a problem with the MAF circuit or Engine ECM however these are much more rare and not suspect at this point.
Do you hear any air sucking sounds anywhere near the engine?

PS- I saw your post above where you already swapped out the MAF sensor for a known good one and tried that already.

Hopefully others have ideas and teamwork, there are a few places to leak unmetered air between the MAF and the manifold and other possible solutions.

 

Thanks for your reply. I can really hear some sounds but am not sure whether they are sucking sounds because of the big noise of the engine. I have made an appointment with a Lexus dealer to conduct a diagnosis on 6th Aug. I hope he can give me a detailed report.

 

I have good news.
I went to the Lexus shop last Saturday and took a diagnosis. After 1 hour of checking, they gave me a report which said the intake manifold had a leakage and I needed to change one. The problematic part is shown in the picture.

The staff told me it was behind the engine so it was not easy to find. They took out the pipe which was not supposed to be taken off so easily. They suggested I change the intake manifold, which would cost me $1850 CAD. I thought it was expensive so I went to the repair shop to handle the problem. The chef used some glue and installed the pipe in the car. I had derived for 2 days and the trouble code did not appear again. I will continue to monitor it.