P0172 System Too Rich (Bank 1)

[jwdsubaru]

I have a legacy with following problem DTC ? DTC P0172 System Too Rich (Bank 1) the IT reading (freeze frame is
4407RW - Subaru_Legacy-Data's
Parameters A/C off condition A/C on Condition
A/F correction #1 -0.107 +0.8%
A/F learning #1 -0.25 +1.6%
Manifold absolute pressure 800 mm/hg 338 mm/hg
Engine speed 691 rpm 818 rpm
Ignition timing +17 deg +15 deg
Mass Air flow 5.67 g/s 5.19 g/s
Rear O2 rich signal ON ON

Part replaced are
OXYGEN SENSOR-2NOS
FAN&MOTOTR ASSY
THROTTLE BODY
ECM

The problem still remains and now car has low pick, when ever we check the spark plug when the MIL comes on the carbon deposit on the spark plug is found

Pl help

[ouch1011]

According to the freeze frame data at idle, the fuel trims are ok. You might try taking your scan tool out for a drive and checking the fuel trims while driving. Usually they have to be +/- 15% to set a fuel trim code.

These cars have big problems with the MAF sensor failing and reading inaccurately, but not failing so much that they set a MAF code. Fuel trim codes and running problems are more common.

Also check the cam timing. If the cam timing is off it can reduce the efficiency of the engine and cause it to run rich, causing a fuel trim code.