Oxy Sensor (too lean), again.

[FadeToBlack]

I was getting an error 44 (O2 sensor too lean) in my vp, took out the oxy sensor and it was covered in thick black deposits, put a new one in and the car ran fine for about a month...now i'm starting to get the error again and the car is running worse and using more fuel.

The error light comes up about 15 minutes into driving and stays on for a bit then goes of for maybe a minute then comes back on, does this for the rest of the trip. If I stop the car and start driving again say 20 min later the light will come on straight away so I guess it's got to do with the engine being warm.

Anyway before I have to take it to the mechanic to diagnose anyone know what I could check?

Oh and I recently did all my coil packs and fixed a blown head gasket which I assumed to be causing the problem in the first place. Plugs and leads are both fairly new.

[Tom_1569]

Why not try replacing the O2 sensor?
In most cases of sesnors faults, its the sensor thats actually buggered.

[immortality]

possibly a dodgy fuel pressure regulator caussing the car to run rich and foul everything up