Just to complete this thread for future readers I have finally found the problem! It was a damaged cable under the battery. It was enclosed in wire ducting and in a box yet the wire inside was somehow broken. Anyway, for future readers replace the sensor as a last resort as it cost me £170 I didn't need to spend! So to summarise:
Symptoms: Significant but intermittent hesitancy/judder under load, especially after changing gear. Rough idling. Fault codes as above. Lambda dropping intermittently to 0.751 randomly for no apparent reason. Higher fuel consumption and excessive CO % volume from exhaust (100x MOT pass value!).
Cause: Faulty EGT sensor, or (in my case) damaged sensor wire.
Solution: Trace wire from sensor to ecu, inspecting carefully for any damage. If wire is ok visually, do a point to point resistance test from sensor to ecu. If it passes this test then it must be sensor. If not then replace wire and test again. Log EGT temperatures and air/fuel ratio to gather data between tests. Temperatures should be less than about 900C and air fuel ratio not less than about 0.80.
Theory: When the ECU can't get any reading from the EGT it assumes the worst that the exhaust is running beyond the acceptable safe temperature limit. In order to combat this high temperature the timing is pulled back and a lot of fuel is dumped into the cylinders at once, flooding the engine and causing the above symptoms.
I hope this helps somebody as when I searched there was very little to no information on the forums as it is not a common problem.
Symptoms: Significant but intermittent hesitancy/judder under load, especially after changing gear. Rough idling. Fault codes as above. Lambda dropping intermittently to 0.751 randomly for no apparent reason. Higher fuel consumption and excessive CO % volume from exhaust (100x MOT pass value!).
Cause: Faulty EGT sensor, or (in my case) damaged sensor wire.
Solution: Trace wire from sensor to ecu, inspecting carefully for any damage. If wire is ok visually, do a point to point resistance test from sensor to ecu. If it passes this test then it must be sensor. If not then replace wire and test again. Log EGT temperatures and air/fuel ratio to gather data between tests. Temperatures should be less than about 900C and air fuel ratio not less than about 0.80.
Theory: When the ECU can't get any reading from the EGT it assumes the worst that the exhaust is running beyond the acceptable safe temperature limit. In order to combat this high temperature the timing is pulled back and a lot of fuel is dumped into the cylinders at once, flooding the engine and causing the above symptoms.
I hope this helps somebody as when I searched there was very little to no information on the forums as it is not a common problem.
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