Hi guys,

I'm new to this site and need some advice.

I bought a 2.2 Astra in June 2009. Ran perfect for 6 months, covered about 10,000 miles.
Parked it up over for a few days when we had the cold weather in December and when I came to use it again it was running like a bag of spanners.
Took it to the garage and turned out the head was cracked where the spark plug goes in cylinder 4.
Had the head replaced (Cost me £940 🙁 ), got the car back and was still misfiring. Took the car back and turned out the head was cracked again. Apparently these heads are really sensitive and over tightening the plugs cause it to crack and leak water.
So the car went back in for another head (fortunately paid for by the garage).
Now I have my car back with a good head, but it still runs slightly rough, worse at idle, and seems to loose all power in between 2500 and 3750 rpm. Really annoying in the wet as when the power kicks in it really does and I cant stop the wheels from spinning.
I have had my friends laptop connected to take readings and the lambdas seem to be acting very strange. When cold they both seem to working properly (reading around 400mv - 500mv) but as the engine warms up the front lambda gives a constant output of 1106mv and the second one drops to about 30mv and fluctuates between 0 and 80mv but never goes past 100mv) the is also the point at which my car runs worst.

I am assuming one of my lambdas are faulty as if I disconnect the front sensor it runs much smoother but doesn't have the power it used to have. I really don't know enough about modern engines to say which one it is without changing it.

The question is which one is most likely to be faulty? or am I best off just replacing both? OR could this be something else and not my lambdas at all?

Any help/advice is much appreciated.

Thanks

Dan