Audi A4 tdi engine intermittent power loss producing black/grey smoke

HELP! Somebody- My 2005 AUDI A4 intermittently looses power while produces black/ grey smoke with no fault code reported. Renewed MAF and MAP sensor, while
reset ECU by removing battery earth for half hour. Checked ECU for water ingress- none found. Cleaned dirty EGR valve and reset 'Service' indicator, occasionally get a load of rubbish random fault codes that clear as easily they come, help somebody please!
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