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I recently got this 2008 IS250 AWD.
I knew it would need some work, and one of the issues was that the CEL, VSC, and TRAC lights were on.
Codes were P0171 P0174 ( lean condition), and P0420 P0430 (catalytic converter efficiency) , among other things.
I was able to clear P0420 and P0430 with the scanner and they stayed off.
P0171 P0174 kept coming back, and there was also the rotten egg smell under heavy acceleration.
I had a couple exhaust leaks fixed, but that didn't help with the codes.
It came with a cold air intake installed. It had an open breather on the nearest valve cover.
LT Fuel trims were around +20.
ST Fuel trims were around -18.
I checked everywhere for a vacuum leak but couldn't find one.
I replaced the PCV valve, the old one was pretty crusty.
It then occurred to me that I had been thinking wrong about the open breather. I thought that would allow air out of the crankcase, but it actually draws air in. That air eventually makes its way through the pcv valve into the intake. I proved this out by removing the breather and there is vacuum present in the hole. That was the vacuum leak I couldn't find.
So I bought and installed a used factory air box and tube.
I did a hard reset on the computer, and now the P0171 P0174 are gone, and fuel trims are where they are supposed to be.
VICTORY!
Not so fast, now P0420 and P0430 are back with a vengeance. I see in the Lexus repair manual that the CAT test won't run while it has P0171 present, so that explains why the P0420 and P0430 stayed off.
So if one has a small breather filter attached to the engine block side of the where the small weirdly double bent hose is connected when in the factory OEM configuration (between the engine block and the side port of the air intake charge tube).
You’re saying I could plug the engine side hole up and all would be ok?
right now I have the air intake charge pipe side hole (the one after the MAF sensor) blocked/plugged and the the engine block side hole I have a small k&n breather dry filter attached. No check engine codes, but sometimes I feel acceleration seems a bit funky. My gas MPG is as good or better than before though which is bizarre. This is on an 2008 IS250. Any thoughts?
I think it depends on the vehicle. If you are not getting lean codes I would think you are alright. If your PVC is clogged it won't pull air in through the breather. I think there are a lot of other variables, especially on a 16 year old car.
In my case I did a lot of troubleshooting before I discovered this cause.
So if one has a small breather filter attached to the engine block side of the where the small weirdly double bent hose is connected when in the factory OEM configuration (between the engine block and the side port of the air intake charge tube).
You’re saying I could plug the engine side hole up and all would be ok?
right now I have the air intake charge pipe side hole (the one after the MAF sensor) blocked/plugged and the the engine block side hole I have a small k&n breather dry filter attached. No check engine codes, but sometimes I feel acceleration seems a bit funky. My gas MPG is as good or better than before though which is bizarre. This is on an 2008 IS250. Any thoughts?
You need to put it back to oem state like the OP stated. You are introducing a lean condition. Also that small breather filter will clog in no time with crank case gases. Basically choking the system. Once this happens you'll have to much pressure. Which you'll start leaking oil at the valve covers, and seals.
If you do go back to OEM state. Reset your ECU to wipe LTFT's.
[QUOTE=padam9997;11327439]I recently got this 2008 IS250 AWD.
I knew it would need some work, and one of the issues was that the CEL, VSC, and TRAC lights were on.
Codes were P0171 P0174 ( lean condition), and P0420 P0430 (catalytic converter efficiency) , among other things.
I was able to clear P0420 and P0430 with the scanner and they stayed off.
P0171 P0174 kept coming back, and there was also the rotten egg smell under heavy acceleration.
OP, have you tried connecting a scanner that can show you live data? You need to be able to see what the reason for those fuel trims is. In my car's case, the MAF sensor (hooked up to the top of the air filter box on the rubber intake hose) was borked. It wasn't reading the correct amount of air, and the engine kept trying to lean it back, so my ST and LT fuel trims were way out of whack. For reference, the trims should be around 0, plus or minus like 3 max.
At a 750RPM idle, the air flow meter reading should be about 2.5g/s. If yours is reading anything way off that, change out the MAF with a Denso unit (I got mine on Rockauto). Do NOT get a non-Denso unit, it will screw up and throw another light.
I just wanted to close out his thread.
I was able to get rid of the P0420 and P0430.
There were some things I didn't like with the Sensor 2 O2 sensors, so I replaced them but that didn't fix it. I was pretty sure that from my scanner readings, the cats are not working the way they should. However, I don't want to spend the money (which we all know is excessive) to replace them.
I tried a couple different extenders on the rear sensors.
Right angle ones from Big Daddies Garage seems to have done the trick.
Codes cleared and have not returned after about 60 miles of driving.
I hope it holds.
I just wanted to close out his thread.
I was able to get rid of the P0420 and P0430.
There were some things I didn't like with the Sensor 2 O2 sensors, so I replaced them but that didn't fix it. I was pretty sure that from my scanner readings, the cats are not working the way they should. However, I don't want to spend the money (which we all know is excessive) to replace them. I tried a couple different extenders on the rear sensors.
Right angle ones from Big Daddies Garage seems to have done the trick.
Codes cleared and have not returned after about 60 miles of driving.
I hope it holds.
Don't see any fitment info, but they are the only ones I see on the site...
Yes those are the ones I used. They were very high quality parts.
The codes never returned, and drive-ability is good, car runs great.
The only symptom left is some rotten egg smell, usually only on heavy acceleration.
My sons just drove it to Colorado from Ohio, and still no problems.
Yes those are the ones I used. They were very high quality parts.
The codes never returned, and drive-ability is good, car runs great.
The only symptom left is some rotten egg smell, usually only on heavy acceleration.
My sons just drove it to Colorado from Ohio, and still no problems.
Ok, cool - thanks for the update. I think I'll give those a try to get rid of P0430 as a last resort before paying for new cats!
I recently had all them codes. I removed the MAF sensor cleaned it with the proper spray let it dry up installed it back and erased the codes using a cheap scanner and everything is gone.
500 miles, zero codes or issues, fact I think it is running much better. Give that a try before anything.Trust me it aint your cats! Second guess is a Faulty Engine Coolant Temperature Sensor.
All, something to keep in mind is that each time the engine is turned off, crankcase oil fumes bleed into the intake and over time, the oil fumes and small amounts of dust making it past the air filter accumulate on the MAF sensor.
The cure is adding sensor cleaning to your PM interval. Keeping In mind that short trips increase the need for this regardless of conventional or synthetic oil usage.
Adding to this, at a lesser level combustion gasses from the open intake valves are sitting right at the throttle body each time the engine is shut off too.
07-16-22, 04:49 AM
P0171 P0174 Solved
MAF cleaning should be part of Maintenance
