Hi I have a 2000 X reg Shogun LWB which sometimes kicks out plumes of black smoke when ticking over - so bad that pedestrians knocked on the window & told my wife the car is on fire on one occasion!

The car has only done 90,000 is well serviced & normally it doesn't smoke at all - at any engine speed but when this happens there is a 'clunk' from under the bonnet and the engine note drops a bit just beforehand.

It embarrassed me by doing it whilst on the ramp for the last MOT and the guy refused to continue the test after it filled his workshop with acrid diesel fumes! He did hear the clunk though, as the bonnet was up, & he started looking around the nearside area of the engine bay as it sounded like it came from there.

I initially thought turbo but that's on the offside and it does seem to be fuel burning rather than oil. She doesn't use any oil by the way.

It's intermittent which is even more annoying because I know if I cave in & take it to Mitsubishi it probably won't do it for them.

Any ideas?