Service Engine Light - Code P1175

Hi Guys

Trying to get ideas of what might be wrong with my car. 2000 540i/6 with ~126k miles. Short story is my check engine light came on. Took it to the local auto place and the code came up as P1175 (fuel trim adaptation additive bank 2 malfunction. Explanation: large vacuum leak on engine).

What's happening is for the first few minutes after a cold start my idle is pretty rough. Every once in a while when the car is moving and I take out out of gear and don't have the clutch pressed the revs will drop to 0 and the engine will die. The problems go away as soon as the temperature gets to the normal running temp.

I have searched around and everything I have found shows that P1175 is accompanied by P1174. I have yet to find anything that shows only P1175 being thrown, which is my case. From reading around it seems it could be anything from the MAF sensor to gaskets/o2 sensors.

I recently replaced the alternator (for the second time, first replacement alternator went bad) a week ago or so and am wondering if the vacuum leak could have been caused by anything I may have taken off and not put back properly (specifically the air filter housing). My dad also decided he wanted to clean my MAF sensor just before I did the alternator. I am curious as to if there is the possibility of that being cleaned or re-installed improperly which could be causing the problem.

tl;dr - CEL throwing code P1175 only. Any help or ideas would be greatly appreciated. Thanks!

How many miles on the pre-cat O2 sensors? If original, you're overdue for replacements.

You could also take it to a shop for a smoke test.

Originally Posted by edjack

How many miles on the pre-cat O2 sensors? If original, you're overdue for replacements.

You could also take it to a shop for a smoke test.

I assume they are the originals, but am not positive. I have all of the service history so I could go digging and find out.

That p code by itself is pointing to your air mass sensor, likely contaminated. You are dead on in suspecting that your dad may have done more damage than good.

Originally Posted by DHoang

That p code by itself is pointing to your air mass sensor, likely contaminated. You are dead on in suspecting that your dad may have done more damage than good.

Yeah, I'm hoping it's just that. Do you think just cleaning it would solve the problem or is a new one in order? Is there any way to test and see if that's the issue? I think I remember reading in other places that people unplugged the MAF sensor temporarily and the rough idle stopped which meant it was an issue there.

Either way I think I'm going to replace my pre cat O2 sensors, seems like something that needs to be done eventually anyway.

Originally Posted by necero

Yeah, I'm hoping it's just that. Do you think just cleaning it would solve the problem or is a new one in order?

I typed /MAF F3 in the bestlinks, and these came up which may help:
- Mass air flow sensor (MAF) & idle control valve (ICV) require periodic cleaning (1) (2) & buying a replacement MAF cheaper than the BMW MAF (RangeRover MAF) (VW MAF) (Hyundai MAF) & cleaning the throttle body (1)

Originally Posted by bluebee

I typed /MAF F3 in the bestlinks, and these came up which may help:
- Mass air flow sensor (MAF) & idle control valve (ICV) require periodic cleaning (1) (2) & buying a replacement MAF cheaper than the BMW MAF (RangeRover MAF) (VW MAF) (Hyundai MAF) & cleaning the throttle body (1)

Awesome, thanks a lot. I was just looking for throttle body/idle control valve cleaning instructions.

Edit: Am I correct in reading that the 99 and up model years don't have an ICV because of electronic throttle linkage?

Correct for the V8.

Originally Posted by edjack

Correct for the V8.

Thanks, just wanted to make sure. Just an update. At work I cleaned the MAF again and let it sit for a few hours before going home. When I started the car to head home the SES light was off. During my drive home, after about 5 miles or so, the light came back on. Would I be right in thinking that means it's a faulty MAF sensor causing my issues? I'm going to change out my pre-cat O2 sensors as well since they need doing, I just hate not knowing what exactly is causing the problem.

Thanks for everyone's help thus far.