Rough Idle, CEL codes P171, P174

[berwaldg]

My '03 Boxster with 50k miles has begun to idle rough and the CEL shows codes P0171, P0174. Autozone OBDII readout shows lean running in both banks; probable cause MAF sensor. I have replaced the MAF sensor and air filter to no avail. Any other suggestions?

Greg

[Loren]

My '03 Boxster with 50k miles has begun to idle rough and the CEL shows codes P0171, P0174. Autozone OBDII readout shows lean running in both banks; probable cause MAF sensor. I have replaced the MAF sensor and air filter to no avail. Any other suggestions?

Greg

:welcome:

P0171 Oxygen Sensing Adaptation, Idle Range, Bank 1 – Above Limit

P0174 Oxygen Sensing Adaptation, Idle Range, Bank 2 – Above Limit

Possible fault cause

- Incorrect signal from MAF sensor

- Intake air system leaking

- Fuel pressure too low

- Volume supply of fuel pump too low

- Fuel injectors fouled

- PCV valve leaks

- Cap of oil filler neck not closed correctly or seal is damaged

[rzucchet]

My '03 Boxster with 50k miles has begun to idle rough and the CEL shows codes P0171, P0174. Autozone OBDII readout shows lean running in both banks; probable cause MAF sensor. I have replaced the MAF sensor and air filter to no avail. Any other suggestions?

Greg

:welcome:

P0171 Oxygen Sensing Adaptation, Idle Range, Bank 1 – Above Limit

P0174 Oxygen Sensing Adaptation, Idle Range, Bank 2 – Above Limit

Possible fault cause

- Incorrect signal from MAF sensor

- Intake air system leaking

- Fuel pressure too low

- Volume supply of fuel pump too low

- Fuel injectors fouled

- PCV valve leaks

- Cap of oil filler neck not closed correctly or seal is damaged

Had this problem today myself and found this via keyword search on the CEL codes. Thank You, Loren!!

[rzucchet]

My '03 Boxster with 50k miles has begun to idle rough and the CEL shows codes P0171, P0174. Autozone OBDII readout shows lean running in both banks; probable cause MAF sensor. I have replaced the MAF sensor and air filter to no avail. Any other suggestions?

Greg

:welcome:

P0171 Oxygen Sensing Adaptation, Idle Range, Bank 1 – Above Limit

P0174 Oxygen Sensing Adaptation, Idle Range, Bank 2 – Above Limit

Possible fault cause

- Incorrect signal from MAF sensor

- Intake air system leaking

- Fuel pressure too low

- Volume supply of fuel pump too low

- Fuel injectors fouled

- PCV valve leaks

- Cap of oil filler neck not closed correctly or seal is damaged

Had this problem today myself and found this via keyword search on the CEL codes. Thank You, Loren!!

Like the OP, I have a 2003 (986) with almost exactly 50,000 miles.

Update: So cleared the CEL memory just to see if they would come back. I did not notice any rough idle before doing this, but I did after I reset the CEL! It had me a little worried. However, after a few drive cycles, the rough idle disappeared. Just when I thought everything was fine, the CEL came on again with the same two codes (P0171 and P0174).

I checked the oil tube filler cap to make sure it wasn't leaking, since that sounded like the most simple thing to replace, but it seemed quite airtight.

I then decided to clean the MAF according to instructions on Mike Focke's site (thanks Mike, if you're reading this). I then cleared the CEL codes, and the same thing happened: very rough idle that steadily improved and went away completely after a couple of days. And when I thought everything was OK, the same two code popped up again. &^##@!

So...Taking a a look at the other possibilities in Loren's post, I don't think (?) I'm enough of a mechanic to mess with the fuel system. So that leaves me with a few choices:

1) I could replace the MAF with a brand new one

2) I could try looking for other intake system leaks, but I don't know how to do this. Can someone point me in the right direction? For instance, the PCV valve, I thought my car has an AOS -- I'm confused on this option, obviously. :huh:

3) I could give up and take it to a mechanic. <_<

4) I could ignore the problem for now since I do not perceive any problems when driving the car.

5) There's probably another option that I'm just missing here.

Any advice greatly appreciated! Thanks,

:renntech:

[Porker]

If you remove the air hose from in front of the air mass meter (so it is still able to measure the incoming air into the engine) and with the car at idle block off the hose with something like a hardback book then this should strangle the engine of all air, and so it will stall, unless there is an air leak somewhere and the engine is able to suck in unmetered air through the leak. If this is the case lets hope is squeals and hisses so you can trace the leak.

If there are no leaks the a brand new air mass meter sounds like the way to go.

It would be great if you could delete the engine adaption values stored in the engine ecu when replacing this air mass sensor, least this will give a better true reading from the outset.

Hope this helps.

[RFM]

@ Porker, the engine actual values are deleted every time you clear the fault codes or disconnect the battery.