2002 phase 2 172 stalling

[jumping]

As above. Car stalls when coasting to a junction or parking when warm. Idles rough when cold but doesn't stall. When warm if I manage to pull up and not stall by giving it a bit of throttle it will idle although very lumpy. Any info would be great guys. As a side note this began to happen after weeks of driving with a large hole in the exhaust. Got it welded and this happens!?!

 

[jumping]

I take it that it's a sensor that's gone. Is there anything I can check or is it a job for the garage and a diagnostic machine?