Hi guys, what are the symptoms of a cracked exhaust housing on a turbo? My mate is pretty adament the car has a cracked exhaust housing but I dont think it does....

Its a Seat Ibiza Cupra with a K04 conversion...out of no where the car has started to idle lumpy and developed a bit of a misfire which isnt there all the time and most apparent on light throttle...the car also doesnt pull as clean as it once did

He has changed his plugs, coil packs both to no avail...it did run a bit better with the coilpacks but the problem is still there

He did notice on of the plugs was properly black compared to the others

He has also told me that there is a bit of smoke that comes from near the turbo area when he revs the car stationary...

Surely if the exhaust housing was cracked there will be a blatent exhaust 'blow'? Or if its cracked internally...would it have this strange misfire/idle problem?

Thanks for any help!