ASX loss of power and smoke and burning smell from exhaust
 

I have an intermittent problem with my ASX3 1.7 turbo diesel. Approx once a month I get a rubbery burning smell from the exhaust which then follows with loss of power and then exhaust will blow light grey smoke and then clears. As this is intermittent is hard to diagnose. I get no engine management light however I'm concerned to what the issue is. Any ideas?