Rock-a-Lex

iTrader: (4)

I have read MANY MANY threads here where several members including myself had on going issues with a PO171 (engine bank 1 too lean) code. I personally have:

- Replaced the air intake filter with new (non-oil type)
- Cleaned MAF sensor and throttle body
- Replaced ALL four O2 sensors
- Replaced ALL spark plugs
- Re-set my ECU
- Used LUCAS fuel injector cleaner for about 4 tank fulls in a row

Most of thes items were done about 2 months ago and JUST today I get this damn code. The ONLY things left to check/replace are:

- bad MAF sensor?
- bad catalytic converter(s)?
- bad/clogged fuel filter?

Are these valid items to look into? I am buying a brand new MAF sensor from Carson Toyota/Lexus tomorrow (Monday). Not a reman, not a generic part, not a used one in "good condition" from Ebay. I want to buy brand new OEM to definitively cancel this out as a possible problem area. I had my mechanic look at the cats the other day and he says they're fine...but who knows. I am pretty pissed off right now.

I will be the ginea pig and change out my 9 year old MAF with a new one. If this works I will report back to you guys. This could solve a huge common issue amongst our members!

speedaddic

iTrader: (10)

with all the time my GS and I have been spending lately I'd recommend checking the fuel pump and injectors as well. I highly doubt it will be the maf (I had this problem a few weeks ago) it was a problem with my fuel setup.

macd7919

iTrader: (10)

Which intake do you have?

GS4_Fiend

iTrader: (22)

Last culprit would be the ECU for the intake. There is a thread about this problem. End up adjusting the ECU for the intake to compensate the amount of air drawn in and it was fixed. If you didn't get an ECU with the intake you are buying, that would be the common probelm. Or you can just switch back to OEM intake. GL.

P.S. - Check for vacuum leaks like from the PCV, brake booster, etc.

Rock-a-Lex

iTrader: (4)

How should I check these items? Thanks

Rock-a-Lex

iTrader: (4)

K&N FIPK for the last 5 years. I have an Amsoil dry media filter on it now instead of the K&N oil type. I also have the Apexi Neo A/F controller on her for the last 2 years or so...this code initially started at least 4 years ago and comes back every once in a while...I havn't had any issues (CEL's) since today for the last year or so.

Rock-a-Lex

iTrader: (4)

I don't have an ECU for my intake. I do NOT have the SRT intake which comes with an ECU.

macd7919

iTrader: (10)

The safc is the same as the Srt except it's adjustable. You could try this, go into the afc and increase fuel 5-8% across the board, see if the code returns with the extra fuel. If it doesn't you could just be right on the borderline of lean with your current map. Sometimes if a map is close to the edge things like weather changes etc...can set a cel off. Worst case scenario you try it and if it doesn't help just return the settings back to how they are now, it will be easy if you just go up a fixed amount across the board as I suggested.

Spyder78

iTrader: (7)

I had the same code popping up or the last 2 years. It was due to an air leak.

Rock-a-Lex

iTrader: (4)

Damn! Really? Where was your air leak and how did you fix it?

Rock-a-Lex

iTrader: (4)

This could definitely be the case! I will try to make these adjustments...although I am scared. Last time I touched something I stalled my car and couldn't start it back up because I hit something on the fuel map and didn't know what I had touched. Not sure if I'm that brave right now. Thanks for your input though.

macd7919

iTrader: (10)

All you need to do is go into the "high" and "low" throttle maps. There should be a graph with different rpm points and a percentage for each. Just raise the percentage up 5% for each rpm point on both high and low. Don't change anything else excepts for these settings, don't change sensor type, inpu/outputnumbers etc.... If you are still nervoustake it to the shop who did the install and ask them to walk you through it, it is a 5 minute job MAX and if they try to charge you tell them to suck one as they are attempting to rip you off.

Rock-a-Lex

iTrader: (4)

...OK guys. I'm going to try something new to rule out the MAF as being faulty. I will disconnect it then start the car and drive around for a little. I heard that this will NOT harm anything. If the car runs fine (or better than before) the MAF sensor is bad. If it runs like a bag of $hlT the the MAF sensor is doing it's job and there is an issue elsewhere. Any objections?

GS4_Fiend

iTrader: (22)

When you disconnect the MAF. It will not monitor the amount of air that is being drawn into the engine. I'm unsure if it's going to do any harm, probably gonna go into limp mode for back up since the computer don't know what to rely on to for fuel trim. Mostly likely the car is going to run rich because when the computer can't measure the air, it's going to be infinite air coming in, so the computer is going to lengthen out the injector's pulse width and make it rich to compensate for it. Which means, the car is going to run very sluggish. But if you really want to check to see if the MAF is at fault. You can do the tap test. With the engine running lightly knock on the MAF sensor, if the idle changes when being knocked, its bad. Or you can do a voltage drop test. You would have to ask someone with a repair manual to upload the procedures and specs.