T4 lambda and poor power

Hi I have a 1998 V40 T4 manual, which seems to have a couple of faults. First is the lambda warning light comes on when you drive the car a little harder than normal. I seemed to fix this by taking all the trunking from the turbo to the inlet manifold off and then refitting it, I was expecting to find a crack or rupture but no nothing. Once refitted the lambda light went off and no matter how hard you drove, it stopped off. It stayed like that for 4000 miles or so, now its coming back on again. Also the car seems to have a reluctance to pull as if it is not producing the power it should. I have tried looking at the waste gate but only managed to actuate it by hand, this also seemed to improve things but only for a short time. I wondered if the lambda light was linked to the poor power, if it was loosing boost preasure after the air flow meter it would over fule the car possibly bringing on the sensor waring light! Also when you put the aircon on, the car holds the revs on when you change gear, so the car is very bad to drive especially around town. I hope i havent gone on for too long but if anyone can help i would be gratful.

Johntyboy.