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Old 01-19-2012, 11:14 AM   #1
Yury
 
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Drives: 2008 5 Door Liftback Auto
Join Date: Oct 2011
Location: Canada
Posts: 157
Why my PCM try to lean the mixture at idle?

Hi All,

I've posted before about sub-par fuel mileage on my 08 liftback. I have been trying to pinpoint the issue and there's one thing in regards to that.

So I hook up an obdII scanner (well it's a bluetooth adapter and Torque on an Android phone...neat) and see consistent negative long term fuel trim at idle. Most of the time it's at -7%. Under any kind of load the numbers are closer to 0.

Here's a typical idle screenshot:



Overall the car drives fine. The measured air fuel ratio is around 14, the commanded ratio is about the same.

Things that have been done recently:
- air filter
- tb cleaning (had some deposits)
- new spark plugs (black base ring on the original ones...rich condition? pic here: http://i425.photobucket.com/albums/p...5700548578.jpg ) New plugs are NGK iridium.
- new PCV valve (oem).
- reset the PCM a couple of times...fuel trim crept back to -7% pretty quick.

Any ideas?

Thank you.
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1999 Honda Prelude Base 5 speed (summer driver)
2008 5 Door Liftback Auto
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