Recurring P0172 and P0175 CELs

[Fixxxer]

Hello everyone. I've had these two faults appear three separate times now, all within about 100 miles of each other, and all when the car has been idling for a short period.

P0172: System too Rich (Bank 1)

P0175: System too Rich (Bank 2)

I've searched the forums, and it seems the likely cause is the MAF, but I wanted to post my Torque Pro logs of when the CEL occurred to see if any of you could help me pinpoint the problem. For what it's worth, I just changed my spark plugs last weekend (after having seen the CEL twice) and inspected the ignition coils, but no problems were found and the CEL appeared again this morning. My MAF looks clean to the eye, but I'm hesitant to use electrical contact (no residue) cleaner on it unless it's absolutely necessary.

The first Torque Pro log below is from just before the CEL occurred when I pulled up to a stoplight. The second log is from a few seconds after the CEL occurred as I was pulling away from the stoplight.

Log #1: Pre-CEL

Time: 04-Apr-2012 09:02:15.096
Speed: 0.979mph
Bearing: 341.0
G(calibrated): 0.00141555
Fuel Trim Bank 1 Short Term(%): 0
Fuel Trim Bank 2 Short Term(%): -1.5625
Fuel Trim Bank 1 Long Term(%): 0
Fuel Trim Bank 2 Long Term(%): -0.78125
Engine Coolant Temperature(°F): 184.99999595
Engine Load(%): 2.35294127
Engine RPM(rpm): 691
Mass Air Flow Rate(g/s): 6.25
Throttle Position(Manifold)(%): 2.35294127
Fuel used (trip)(gal): 0
GPS vs OBD Speed difference(mph): 0.35807136
Transmission Temperature(Method 3)(°F): 184.99999595
Acceleration Sensor(Total)(g): -0.01302952
Acceleration Sensor(X axis)(g): 0.00555366
Acceleration Sensor(Y axis)(g): -0.03887559
Acceleration Sensor(Z axis)(g): 0.01943775

Log #2: Post-CEL

Time: 04-Apr-2012 09:03:56.093
Speed: 5.597mph
Bearing: 2.0
G(calibrated): 0.06632715
Fuel Trim Bank 1 Short Term(%): -3.125
Fuel Trim Bank 2 Short Term(%): -7.8125
Fuel Trim Bank 1 Long Term(%): 0
Fuel Trim Bank 2 Long Term(%): -0.78125
Engine Coolant Temperature(°F): 197.59999561
Engine Load(%): 10.1960783
Engine RPM(rpm): 823.5
Mass Air Flow Rate(g/s): 9.75
Throttle Position(Manifold)(%): 14.11764717
Fuel used (trip)(gal): 0
GPS vs OBD Speed difference(mph): 0.62137121
Transmission Temperature(Method 3)(°F): 197.59999561
Acceleration Sensor(Total)(g): 0.03373463
Acceleration Sensor(X axis)(g): 0.17216341
Acceleration Sensor(Y axis)(g): -0.31378168
Acceleration Sensor(Z axis)(g): 0.13189937

Thanks for any help you all can provide!

[logray]

Hi there!

Check out this thread, I think it has all the answers for you:

http://www.renntech....t-safe-to-drive

Also ensure the plugs you bought were of the correct type and if they required gapping, the gap was set properly.

This looks suspect to me and matches why codes were thrown (but be careful because Porsche doesn't use short term fuel trim, you will see these numbers do not match up if you read the TRA (RKAT) from a durametric/pst2:

Fuel Trim Bank 1 Short Term(%): -3.125

Fuel Trim Bank 2 Short Term(%): -7.812

Edited April 4, 2012 by logray

[Fixxxer]

Thanks for the reply! I actually saw that thread in my search - I just wasn't sure if the fuel trim data I captured would help pinpoint the problem.

BTW, I've also looked for air leaks and found none.

EDIT:

The plugs that I installed were OEM and were gapped properly. I was receiving the same CEL before the plug change, so I don't think it's related.

That's interesting that Porsche doesn't use STFTs. I didn't know that!

Edited April 4, 2012 by Fixxxer

[Karl996]

I'm not saying it's right or wrong but your MAF flow rate is identical to mine when at idle.

What I do notice is different is that at idle your Throttle Position is at 2.35%. I always thought normal idle was like 10 to 12%.

Assuming the hardware i.e. MAF, plugs etc are okay I would look for air leaks post the MAF.

Edited April 5, 2012 by Karl996

[Fixxxer]

Thanks, Karl. That is very interesting. I tested my MAF last night using this method, and it checked out just fine. There's something else going on here... I'll check again for air leaks.

[Fixxxer]

Okay, this is still really troubling me. Last week, I disconnected the battery for about 30 minutes, thinking that a reset of the ECU might help it re-learn everything properly. Unfortunately, the very next day it popped another CEL (same as above) on my way home from work as I was pulling up to a stop sign. Something is really screwy here... It shouldn't be an O2 sensor, a vacuum leak, a leaking fuel injector, or a stuck Evap purge valve, because any of those would either be throwing different fault codes and/or only affecting one bank.

That only leaves the MAF or an air leak. I've checked and can't find any air leaks. Plus, if it was an air leak, it wouldn't be happening so randomly and only at idle, would it? When I tested the MAF voltage at KOEO (Key On Engine Off) and at idle, the readings were right where they should be: 0.9V - 1.0V at KOEO, and 1.45V at idle. However, when I revved the engine a bit (around 3,000 RPM), that figure came up to around 1.8V. Is that normal, or should it remain at 1.4V through the RPM band?

If it's not the MAF, what else does that leave? Any help would be greatly appreciated. This is driving me nuts!

Edited April 9, 2012 by Fixxxer

[Loren]

P0172 Oxygen Sensing Adaptation, Idle Range, Bank 1 – Below Limit

P0175 Oxygen Sensing Adaptation, Idle Range, Bank 2 – Below Limit

Possible fault cause

- Incorrect signal from MAF sensor

- Fuel pressure too high

- Fuel injector leaking

- EVAP canister purge valve open

We've seen a lot of these be a faulty canister purge valve. Worth checking I think. Do a search here for more info.

[Fixxxer]

Just for giggles, I replaced the stock airbox this week (it had a K&N FIPK installed from the previous owner) and cleaned the MAF. My first impressions are that it's running better/stronger, but it could be my imagination. I'll pulled some OBD2 data on a couple of short trips, and the LTFTs look okay - still no CELs. I'll keep an eye on it and report back if anything strange happens.

[Fixxxer]

Still no CELs! I think cleaning the MAF is what did it. The car is still running much better than before, especially when starting from a stop (I have a manual trans., not Tip). I still wonder though, how could a dirty MAF cause a CEL to only occasionally show up? Shouldn't it appear the next time I drive after it was reset? Weird...

[logray]

A MAF could be marginal and cause CEL, or even cause a pending fault which will not light the CEL, but will be stored in the DME. The engine mananement system will store a pending fault until a certain number of occcurances or situations are met, at which time it can either remove or pending fault (problem corrected itslef), or light the CEL.

[Fixxxer]

Interesting. Thanks for the info!