Black smoke comes from exhuast when engine gets hot

Take it to the VW dealer quit wasting your money !

Could be valve stem oil seals, could be piston rings worn, could even just need a tune, best advice without seeing the car run is to go to your local mechanic with the car for their opinion

Faulty exhuast cam actuator control solenoid.

Engines runs for a couple of seconds then loudly backfires with a flash of flame out of the exhaust followed by a plume of black smoke. Then runs sort of ok for a couple of seconds then repeats the backfire again AmanStino Lightning Cable Apple MFi Certified 1M Nylon Braided Charging...

You need a Repair Shop,just by the
way your question reads

Hi! You may have a faulty ECU (engine control unit). The ECU controls the air and fuel ratio, if its faulty it can really emits black smoke. Hope this helps and good luck!

Well if you have white smoke when reving up engine then its not smoke its STEAM as you have been lossing coolant by the sound of it (yes) or no,,,,IF yes then you have done a head gasket or something else which
is letting in coolant to the cylinders and when it fires it blowes it out the hot exhaust and causes steam ,, as the only other way to get white smoke could be burning brake fluid/ or kerro.
So does your engine get hot /loosing coolant/missing when running ///any of these will cause your problem.
Let me know how you get on ,, Ron

ya its running very rich that why it makes that black smoke,this carbon is made because the sparks plugs does not make a good and sufficient spark,so i advice u to change the 4 spark plugs,also renew the air filter

You probably have a service engine light on too. It sounds like your CTS (coolant temp sensor) isn't working and causing the injectors to run rich.

black smoke from exhaust means a rich oil/fuel ratio, sometimes it causes by a clogged air filter or a problem on fuel injection system.