I need help and advice. A while back I was getting a CEL and its code was PO171 (engine bank #1 too lean). I went to my mechanic and he was hesitant to work on my car because of my air intake. He mentioned that it was probably my O2 sensor. I told him that I'de rather him work on it than the Lexus Dealer because of their high price. He said he would only work on it if I sign something stating that if the CEL does not go out he cannot be held responsible; I agreed because I didn't know if my intake was the cause of the problem. Anyway, he replaced the O2 sensor and guess what... the damn CEL came on again. I drove back to the mechanic and they checked the code; still PO171 (engine bank #1 too lean). What the hell??? He told me to clean out my MAF (and be delicate about it). I searched on this forum and found suggestions to spray rubbing alcohol and use Q-tips carefully; so I did and also reset my ECU. About 5 miles into driving the CEL comes on again!!! What can this be??? Can my MAF be bad, how can I tell? Also, how would I know if my custom ram air setup to my intake isn't the real culprit. I don't want to replace the MAF or the "other" O2 sensor (there are 2 O2 sensors regarding A/F on the GS) just to find out that I'm changing out good parts. Please advise!!!

 

Here is some info.

1. 9 times out of 10 if you have a bad maf you will get a code that says it is bad same for O2 sensors.

2, I would check the gaskets around the Maf and make sure they are okay also check all the hose clamps after the maf that connect up the intake pipes.

Make sure that all the wiring for the SRT ecu is still in place and properly connected.

Well actually that brings up another question, what type of intake are you using. Is it newly installed? Does it come with a computer to compensate for the additional air

 

How long have you had the intake on before getting the CEL?
Check your MAF gasket. A test before you replace the MAF. Disconnect your 90 degree 3.5" pipe and connect your air filter back to you K&N in take. in other words put it back to stock and clear the code.
My guess is that it is the 3.5" pipe you've added. All intakes for the GS that I'm aware of are 3" or smaller except for the SRT which is 3.5" and they add an ECU to add more fuel to help avoid any lean issues.

 

He has a custom intake. A K&N w/ a 3.5" cold air intake pipe added.

 

Pretty sure that the intake is the problem, he's getting too much air and the ECU `cant compensate.

You could always throw an SAFC on to help tune it.

 

Thanks for the response guys. I really appreciate it. I bought the original K & N FIPK about 2 years ago (it has 3.5" piping throughout the entire system). I extended the intake last May (90 degree bend into the wheel well, also 3.5"). The car was fine, then around September I modified my lower air dam (sliding door mechanism) for a ram air effect. Coincidentally after that my car has popped a CEL. Still runs good ... but has a CEL. I can't have that, especially if I want to pass an inspection next time around. I first thought that the CEL was because of my intake (it would make sense), however, there were a couple of members at the LOC forums that say the stock MAF should still compensate for the additional air on its own. I don't think they understand my setup with the ram air effect. I'm pissed; I just had one of my O2 sensors replaced (list price of $215.99 and 1/hr labor @$80). So after spending $332.xx (after tax) my car is still popping a CEL! It makes sense for me to test the car without the 90 degree bend as GILLEXUS suggested however... If this does correct the problem I am still going to want to find a way to still put my extension on and have it run properly. Morris, do you think the S-AFC controller will really correct this problem??? If my CEL has to do with A/F readings I agree that this could fix the problem. Coincidentally I was thinking of getting an S-AFC so I can tune it like the settings on SRT's race ECU. If I was going to install the S-AFC should I just do that first anyway??? If there is in fact a problem with my MAF will and can the S-AFC do its job correctly??? BTW the black rubber/foam gasket around my MAF looks fine to me a little flattened but no cracks or boken pieces. Thanks.

 

The SAFC can ussually compensate for additional airflow from an intake. If there is something wrong with your MAF sensor though it will not compensate for a faulty sensor.

I try to keep the number of changes to my system to a minimum when troubleshooting. Particularly when you do not know what the real cause is. I would probably try to return the intake to stock and see if that solved the problem. This way I would know for sure and I wouldnt have to troubleshoot the issue with additional unknowns like the SAFC. Once you get the SAFC in you may have to troubleshoot that, (things like is it wired correctly, is it tuened correctly, are the settings set correctly etc.)

 

Wow you paid $215 for an o2 sensor. next time try sewell or Carson Toyota, might get it for about $125.
Are ou sure your K & N intake pipe is diameter 3.5"? it look a bit smaller than the SRT pipe I have.

Your right that the stock ECU and MAF should compensae for the additonal air and yours might not be affected that much by it since it is running ok and not stalling out or sputtering. The ECU has it own A/F parameters and migh tbe running lean a few times whille dring to set the CEL off.
I know it sound odd but when you take off the baffle on your air filter it is probably getting too much air for your stock ECU.
Put the stock K& N set -up on and see if that gets rid of the CEL.

I would narrow down the CEL cause first before adding the S-AFC.
Get a good tuner to tune your S-AFC (some -one that knows what they are doing)

 

I will take off the extension as soon as I can; then troubleshoot from there. Hopefully I can narrow the problem down. If the problem is fixed after I remove the other part of the intake then my MAF is OK...right??? If the MAF is OK and I put the extension back a properly tuned S-AFC should get rid of that CEL. Is this correct? BTW I got quoted from a reputable shop around here for supplying and installing the S-AFC along with 3 dyno pulls for around $550 - $600.

 

Usualy the P0171 code is for faulty meter. It can also be a leak between the meter and the motor. If there is a crack in the intake pipe it could mess up the reading as well. On older ES's the pipe between the meter and the throttle body can crack and throw the same code.

 

BTW it can't have anything to do with the spark plugs right??? I was just thinking that I installed Torque Masters back in October...right around when I started to pop the CEL. But the car runs great and is smooth at both idle and driving. What do you think???

 

yesterday i removed k&n kit and i installed my srt kit, just piping and filter. i was planning on doing the same thing as rock a lex with the extesion part. after i installed srt, i test drove the car and it ran fine. it felt a little slower for some reason, but i thought since i have the trunk full of junk and a full tank, that maybe the reason why my car felt slower. this morning i drove to work and everything seemed fine. after work i was on my way home and my engine light came on, car still drove ok. i went to my pops shop, hooked up the code scanner and i got PO171 engine bank #1 too lean. so i removed my maf, cleaned it, reset ecu and test drove. cars was runnig bad, bogging out and check light came back on. the car smelled like it was runnig rich and i killed 1/4 of a tank in about 50 miles from yesturday to today. i put the k&n kit back on, reset codes and car now runs with no prblems and feels faster. i am with you rock a lex i will find a way to make a true cold air kit work. rock a lex keep me posted on any result. i am going to wait until i get a wideband to see exactly where my fuel ratio is.

 

Sounds good GSFonzy...I feel K & N is the best (in my opinion). SRT is great but I don't like the fact that it comes with a piggyback ECU preventing you from buying an A/F controller (such as the S-AFC) in the future. You can get the maximum out of your intake/exhaust setup by tuning an S-AFC as opposed to a preset non-tunable piggyback ECU. The SRT intake is still great if you are not planning on having the S-AFC installed. This weekend I am going to take my extension off and monitor the check engine light. The O2 sensor is replaced and MAF is cleaned. If the CEL indicator is still present I will go ahead and install the S-AFC to see if this will solve the puzzle.

 

Just for anyone that reads this thread inthe future.

DO NOT Stick or Spray any high pressure aerosols into the Maf sensor, you will very likely damage it.

There is something very similar to a filament inside the MAF it is very fragile

If you do want to clean it spray from a distance into it so that the pressure is not high

 

i thought our maf would adjust air fual ratio according to n/a flow, but guess not. i feel challenge to find out what causes the light to go on. i will try to get some info this weekend, throl pos, flow, int temp, timming and see what changes in the two. the kits are almost identical, i don't know why something like this can happend. i guess we got to thank lexus for making such a complex car.