Bluejay84

First, I realize what I've done may not have needed to be done, or should I say in hindsight obviously didn't need to be done as the problem is still haunting me. I figured I could chase the problem like a lot of mechanics seem to do in the posts I've read, I'm also not slamming the mechanics as it seems this can be a really difficult code to fix. I'm hoping to get some suggestions for a logical order of things to check and replace next. Thanks for the help!

1. Checked hoses for cracks and tried the carb cleaner diagnosis. Didn't seem to get any revving of engine. I did replace a couple of hoses as there were cracks over the connection but not outside the connection. Also checked the hose behind the air box was connected. Reset the code and it came back pretty quick.
2. Cleaned MAF. Reset code. Code tripped again after a few starts. Replaced MAF. Code came back after a few starts.
3. Rechecked hoses. Found the clamp closest to the MAF was loose. Tightened it. Reset code. Lasted about three starts. Tried to reset code in hopes that maybe the computer was still relearning / resetting. Drove a little over two hours on the interstate and a couple of more days around town. Code tripped again this morning on my way to work.

If you can help me create a list / order of things to go after next I would appreciate it. Feel free to tell me to call no glory and just take it to the pros. My concern there is that I'll dump a lot of money into labor with the same results.

Thanks for the input.

Bluejay84

Hopefully this follow up will get a response. My last "fix" included replacing the hose going to the PCV (it seemed like it didn't fit real tight - but didn't have any cracks) and reset the boot resonator where it attached to the intake (one side wasn't pushed all the way up snug). Keeping my fingers crossed and just when I was starting to get hopeful, 12 days after resetting the code the CEL came back on and tripped another P0171.

My questions:
1. Wouldn't something "obvious" trip the code a lot sooner than 12 days?
2. I had just filled the tank, made a less than 2 minute trip across the street to shop, and within 2-3 minutes of heading home from shopping the code tripped. Could something be associated with the code and a fresh full tank of gas? Fuel pump or related?

I'm starting a log to try and figure out if there's a pattern to the problem. This is very frustrating and like other guys have expressed, I'm really regretting ever getting this car. I take a fair amount of pride in keeping my cars in good working order and am bewildered at how difficult this is to resolve. Hopefully I'll get some responses instead of just views this time and can make this thread constructive for both me and anyone searching it for constructive advice.

salimshah

What is making you chase the vacuum?

Since the problem is on one bank, I would concentrate on that particular ban .. MAF is common to both banks.

Other thing I would suggest is to hook up live data monitoring and share the data with expert [this is out of my league]

Salim

Bluejay84

What live data should I get numbers for and under what conditions? Idle, acceleration, ...?

Thanks.

artbuc

Lexmus

Check the fuel trims. That P0171 code triggers when the trims on bank1 are over 25% (approx). On my RX, even though only bank1 was indicated bad by the code, both banks had excessively high fuel trims (over 20%) when I checked, but one bank was slightly higher than the other. I replaced the MAF, the fuel trims reverted to much closer to normal, and the code has not returned. FYI, the corresponding bank2 code is P0174.

To check the fuel trims: get a bluetooth (android) or wifi (iphone) OBDII reader and OBDII app. I use the Torque app for android, which ever app you like for iphone. The fuel trims are available to read and lead you to the proper fix.

This is the OBDII reader I use:

Lexmus

You want to check the trims at idle and at roughly 2000 rpms. The exact rpm value is not critical.

salimshah

Thanks Art. Maybe OP needs to make measurements [ohm/voltage ..spec can be searched over the net] and just replace the MAF .. sometimes the cleaning is not the solution, specially if the sensor has gone bad.

Salim

artbuc

Bluejay84

I checked the trims and I think they look good. They balance out with the highest being about +6% on long term. I have a diagnostic so can check a lot of different things. Any suggestions on what to do next? As stated in my first post, I did replace the MAF (denso) and both A/F sensors. I really appreciate the help and best guesses as I'm at a total loss and completely frustrated.

Lexmus

I thought a P0171 is only triggered if the trims, especially the Long term, was high, on the order of 25%. If you have normal fuel trims from idle to high speed I don't see how that code could be thrown. You need to monitor the trims continuously to see if/when they spike and under what conditions.

salimshah

There comes a time where one has to pay the piper [dealership]. Keep in mind, here we are enthusiasts and not trained and qualified techs.

Salim

artbuc

Bluejay84

LIVE DATA!
Here's what I'm seeing with some live data. The fuel trims seem to be spiking when I let off the accelerator at lower speeds, specifically between 15-20 mph up to 35 mph, when coming to a stop or just getting off the gas for about a 10 mph drop and then accelerating again. They settle back to "normal", meaning ST near zero or 1-2% and LT staying under 8% at a complete stop and maintaining any speed. I've had "regular" spikes in the 10-15 range and a couple at 20 with one as high as 28. The CEL hasn't tripped yet after several trips over 10 days and my last fill but I'm expecting it to light up again soon.

Does anyone have ANY idea what would be causing this?