My 1.9 TDI has recently started pumping blue smoke, but the symptoms are a little strange (to me) and don't seem to match up other threads on the subject.

Here goes:
  • Blue smoke only at tickover and low revs
  • No blue smoke when accelerating hard or when cruising
  • No alarming oil usage
  • No loss of power, flat spots or fuel consumption
  • Smoke levels the same when hot and cold
  • Very occasional cold start problem. It immediately starts and then stops. Needs about 10 seconds of cranking to get it going.
There are a couple mitigating circumstances
  • The car was recently accidentally filled with petrol, run for about half a mile (oops)
  • Fuel was drained, flushed, fuel filter changed, refilled with diesel
Now I'd accept that there may have been some bore/ring/valve stem wear with running on petrol, but why does it smoke only at low revs and not all the time. Also, the oil level is not consistent with the amount of smoke - to my eyes.

Any thoughts?