Denvermgb

Oh, and very nice write-up! I bet Lexus would have charged a BUNCH to do all this!

ofdave

Thank you, I've only been screwing with this for 9 months. Replaced about the same including converters, couldn't figure out for the life of me why LTF was running at 56% was getting ready to swap ecu's when I found your thread, checked the linkage ... yup, nice and loose Thanks again!

joeangel

Hey, I think you may have just saved me a ton of time and frustration chasing the same 2 codes. I moved the control valve when the engine was at idle and it smoothed out. I cleared the code and it hasn't returned. So we'll be watching this one and will replace the control valve if it returns. Thanks a million for posting this.

Sekumed

Thank you many times over.

I was finally able to locate the problem.

DeeFlat

I am having this issue. No codes yet but he battery was dead


it has a very pulsating rhythm when it gets below 1100 rpm or so above that it is fine. Was this also the case for you ?

koehler5

I have a Check Engine and VSC Lights lit on my 2004 Lexus RX330 with 275,000 miles. My mechanic says that I need to replace both catalytic converters at a cost of $2300! I took it to both AutoZone and PepBoys to see what codes they read and here they are; P0174, P0171, & P0037. AutoZone recommends that I replace the Mass Air Flow Sensor and PepBoys says that they would need to take the car in to diagnose it further. I'm not confident that my mechanic that is saying I need to replace both catalytic converters is troubleshooting this issue correctly. Any I suggestions.....

RedGemini

Odd. Those aren't even close to the codes that most hack mechanics/parts stores want to throw new cats at as a fix. The codes for that are P0420 and P0430. You could try cleaning the MAF sensor with proper spray cleaner. The throttle body may need cleaned as well. Both can be done for under $20 worth of spray cleaners. SeaFoam Spray is great for cleaning the throttle body, though it's tricky without a second person helping. There's a video by SeaFoam showing the proper way to use it. I'll be doing it to mine soon.

AliDXB

I pUT a for sale sticker on my LS430 year 2005 because of this P0174 issue as it turn off the Traction and I hated that!!
I did what you did changed and cleaned everything leak related now I'm gonna try this and hope.it works 😐 I don't really want to sell it been with me for 5 years now

harkirath

I had this on my 04 330 with 250k miles. I reset the codes to see if they came back, and they did after a while. I repeated this process 3-4 times. Now it has been about 6 months with no codes. Car seems to be running fine.

tempestv8

They say that successful people have one personality trait that is key to their success. And that trait is called "grit", also known as perseverance. Well done, and thanks for sharing this information!

caverman

My '01 GS300 just came up with these symptoms. Car had been running great and then all of a sudden would hardly idle. Reading the codes I got P1349 along with P0300-P0306. After going through most of this tread (way too long to read it all), I decide to pull the trigger and just buy a new OCV ($26 shipped) and a OCV filter ($10 shipped). For $36 I figure it's worth just replacing them and hopefully that fixes the issue.

Last year I replaced all the spark plugs, coil packs, and coil pack clips. I'm hoping the miss fire issues are all related to the OCV. Parts are due to arrive tomorrow so I will hopefully know something in the next couple of days.

phimane

I also had the P0171 and P0174 codes on an 2004 RX330 with 220,000 miles. I checked all vacuum hoses, and looked for cracks in the air box. I found none and hoses appeared good. I then purchase the air control valve like the original poster and installed it, and that did not solve my problem. I then replaced all vacuum hoses and made sure to use hose clamps where I can. The problem persisted. I then cleaned the Mass Airflow sensor again, and the problem persisted.

I even check the evaporative valve to make sure it was functional since it has a hose connection to the air intake. There was no vacuum leak in it.

On my one of many test drive, I got P0171, P0174, P2198, and P0420 from an OBDII reader and Techstream.

P2198 was o2 sensor, bank 2, sensor 1. Easy to get, and I replaced it. I decided to also swap out to a known good Mass Air Flow sensor from a neighbor's Toyota Tacoma, since it was the same part number.

P0420 was catalyst no efficient and Toyota TechStream said Bank 1 Catalyst was not passing the test. I left this alone, and started to check prices for the exhaust manifold. This would be ugly if I do end up needing it.

I took it again on a test drive. In the 2 hour test drive, no check engine light! Usually, I would get it within 20 to 30 minutes of driving in varied conditions. This is good news.

I plugged in the OBDII reader anyhow, and I had 1 pending code of P0306, which is misfire on cylinder 6. This was also easy to get to. I bought 1 new ignition coil and replaced it.

I then swapped back to my old Mass AirFlow sensor, and suddenly, all of my previous issue started to come back. I drove a short distance, and plugged in the reader, and it had P0171 and P0174 pending. This told me, the Mass Airflow sensor was the issue. Even with multiple cleaning before, it turned out to be defective.

I bought a new mass airflow sensor, and did the drive test, concentrating on trying to complete the drive cycle, and all was good. No check engine light, and the code reader reported that all the Readiness Monitor was completed. I had a green light on the emission portion on the OBDII reader. Since the Readiness Monitors are completed, and I am green, and I have no more Check Engine light, I can take it to smog and pass.

The root of the problem for me was a bad Mass Airflow sensor. Cleaning it did not help. Replacing it was solution. In the end, I did not spend too much on the ignition coil, O2 sensor, and Air Control Valve to resolve the codes. The car definitely runs smoother, less exhaust smell, and more quiet after resolving the issue.

All in all, I did receive this car for free from close friends who had it sitting in their garage for over 6 months due to failing smog. Lexus wanted to replace the catalytic converter, and we all know it is an arm and a leg. They didn't want to invest money into it. Nobody else wanted the car when they asked around who wants it for free. I was bored so I took it on as a challenge. My neighbor and I took the challenge and was able to solve it. It took me 2 weeks to get this problem resolved. The car is in fair to good condition, just needs TLC.

pchouston

jlexrx

***Change air filter use fuel injector cleaner 1st***

I got both p0171/p0174 on 2006 rx400h @ 137k miles. Researched online both codes together most likely intake leak (air/fuel lean). If no intake leak next step replace air filter/clean MAF sensor could possibly be 2 upper O2 sensors (the expensive ones). I suspected a leaky hose but I cant tell or have know how to test so I did what was easy. 1). Cleaned out MAF with CRC cleaner and replaced both air filter/cabin filter (haven't svc car in 45k miles). Air filter was pretty darn dirty!!!. Reset CEL it came back a week later. 2). Swapped out MAF sensor from my other Toyota & used 12oz bottle Chevron Techron Concentrate Plus Fuel System Cleaner. Also pumped 91 octane normally pump 87. Reset/light came back a bit over week later. At this point I knew it could be a sensor or something needs cleaning since CEL took longer to go off. If it was something urgent light would go off right away. Asked my mechanic he said its Air Fuel Ratio Senor which are those expensive upper O2 sensors and go w OEM. Rather than spend over $100+ each. Decided to give fuel injector cleaner another shot. 3). 1 bottle Gumout High Mileage Fuel Injector Cleaner. Now so far so good 1500+ miles/3+ wks no CEL. It could be dirty fuel injector...who knows. I also thought it was air intake box since previous mechanic that changed filter didn't clip in correctly and now the edge of box is kinda bent.

Long story short do some research/mess around/learn something new. I guess you could say Im a believe of the fuel treatment "snake oil" every ones situation is different of course. What worked for me might not for you but I wanted to share my experience save those time or $$$ from mechanic. My rx is probably worth 6-7k and it didnt make since to drop 1-2k on repairs. I rather try figure out the problem 1st. Good luck!!!

reisingdw

Excellent write-up. Congrats on your discovery.