Hi there hope i can be of assistance.
Ok, this may be related to the work that has recently been carried out. So i would advise that you take the vehicle back to the workshop who carried out the work.
However, from what you describe this sounds like a fuel pressure/metering fault.
The usual suspect is the fuel metering valve. If this is fault it will cause low fuel pressure, which means less fuel to the injectors causing black smoke (excess of air).
Further diagnostics are needed as there are many possible causes of this. We can only advise on the most common of faults as we dont know the actual fault codes that are now on the engine managemtn system that would give a clear indiocator as to what is going wrong.
A good place to start is with the previous work that has been carried out, ensuring no multiplugs, pipes, wiring etc have come loose/chaffed.
The most common cause is the fuel metering valve, but further diagnostics will need to confirm this. I cant give you a 100% accuarate answer here, without further diagnostics.
Ok ill opt out, and open the question to other experts.