Fuel economy S***e Lambda sensor US?

[IG]

My sons 2L GTI has poor fuel economy and occasional mis fire since he bought it. Got hold of VCDS and below are the following codes that have been generated in 1 week after clearing the originals. I've checked the connections under the OS sill and appear ok. Am i right in saying this is the sensor after the Cat and not the one in the manifold? Has it failed or can you clean it?

Cheers.



Monday,30,August,2010,14:33:44:46862
VCDS Version: Beta 912.0
Data version: 20091201

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Address 01: Engine Labels: 06A-906-018-AQY.lbl
Control Module Part Number: 06A 906 018 EF
Component and/or Version: 2.0l R4/2V MOTR HS V04
Software Coding: 00031
Work Shop Code: WSC 00490
9 Faults Found:
16525 - Oxygen (Lambda) Sensor B1 S2; Heating Circuit: Malfunction
P0141 - 35-00 - -
16524 - Oxygen (Lambda) Sensor B1 S2: No Activity
P0140 - 35-00 - -
16518 - Oxygen (Lambda) Sensor B1 S1: No Activity
P0134 - 35-10 - - - Intermittent
17536 - Fuel Trim; Bank 1 (Mult): System too Lean
P1128 - 35-00 - -
16523 - Oxygen (Lambda) Sensor B1 S2: Response too Slow
P0139 - 35-00 - -
16500 - Engine Coolant Temp. Sensor (G62): Implausible Signal
P0116 - 35-10 - - - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - - Intermittent
16685 - Cylinder 1: Misfire Detected
P0301 - 35-10 - - - Intermittent
16555 - Fuel Trim; Bank 1: System Too Lean
P0171 - 35-00 - -

 

[27litres]

B1 S1 is pre CAT. B1 S2 is post CAT.
O2 sensor readings used in fuel mixture by the ECU are the ones in the manifold before the CAT. The ones after the CAT are used as a reference to ensure the CAT is working correctly and have no direct relevance to fuel/air mixture.
It would seem you've at least got a broken heating circuit in your post CAT sensor, which I doubt you could fix. But both sensors appear not to be working, which would leave the engine in open loop configuration (ie with the choke out!). That would explain poor fuel economy.
That misfire may or may not be related to fueling, depends how clogged the sparks are.

I'd be replacing both O2 sensors, spark plugs and the coolant temp sender, than see where you are.
If the misfire is still there, try replacing the spark leads - as the misfire is all cylinders and intermittent, I wouldn't think coil packs are to blame.