P0171 but not causing problems

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sparer

New Member
Joined
Jan 4, 2012
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13
Car
C200 Kompressor CL203
Hi,
I have a CL203 with an M271 engine which keeps throwing an engine light. When I scan it I get P0171 however I don't notice a rough idle or anything detrimental. It came on right after it's MOT which it passed including the emissions. I checked for vacuum leaks and can't detect any. The Short Term Fuel Trim is at 25% at idle, 25% at 2k rpm and 15% at 3k rpm. Goes to 0% when coming of the throttle. The MAF shows 2.1g/s at idle 9.1g/s at 3k rpm. I've measured the post cat lambda at 425mV and this only moves by a few millivolts if I rev the engine. I didn't know the connector for the pre-cat lambda was under the car so I haven't measured that yet and I suspect it may be the cause, however, is there anything else I should check?

Thanks
 
Remove the air box, I’m sure you’ll find a split engine breather pipe under there.

Pretty common on these 😉
Do you mean this one (in the photo)?
 

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Here’s a photo of the pipe with the air box out
 

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Here’s a photo of the pipe with the air box out
Yep. Mine had a hole that you can see in the photo and also where it attaches into the block. It had just about fallen to bits. Bought a new one from the main dealer for less than £10. Part code is A271 018 12 82.
STFT does what it's supposed to now. Thanks for your help with this Dodipops
 

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