Hi can anyone help please. Symptoms are, lack of power on acceleration, then clouds of black smoke out of the exhaust and plenty of power when this clears. It's an intermittent problem which can vanish for a couple of days and then re-appear. Switch the engine off and it will vanish once again - sometimes... Driving me looney as I don't know if I am doing any damage to the CATS.
Fault code readings are:

P004b
P0299
P0402.

I know it's something to do with the B turbo solenoid and the other two I think are after effects from the first problem - turbo boost fault and MAF sensor readings.

Please help as I love the car and need to get it fixed.

Thanks
Martin