Loss of power and cutting out. Spanner sign warning light?

We have a Vauxhall Vectra Elite Diesel Estate, manual. 53 plate. 39,000 miles on the clock.

Description of problem.

Warning sign on dash of car with spanner through it.
Intermittent problem - car stalls or loses power and black smoke from exhaust.

When revs are low the noise from the engine is like surging. May suddenly stop and revs pick up again.

We have had the car to a garage and a test was done on it and some sensors were disabled but problem still the same.

Very worrying as we pull a caravan and when the car stalls especially on a fast road it is very dangerous.

Other problem - maybe not related(?) Cruise control will not engage sometimes.