P042F (Powertrain) - Help :(

HELP

I was driving along the other day in my 2007 Fiesta 1.6 TDCi and I noticed my exhaust noise got more noticeable and then noticed I couldn't hear my induction/turbo spool noise. Gave it a boot-full and there was very very little boost, if any. Opened up Torque Pro and it wasn't reading boost either. Scanned for faults and 'P042F - powertrain' came up. Apparently this meant EGR valve stuck closed which I thought was odd as I always believed my egr was blanked.

I disconnected the maf and the boost came back and the car ran better, not as good as it used to but definitely better.

I thought the maf sensor might be at fault so I bought some proper cleaner and cleaned the sensor up. I also cleaned the butterfly valve just before the intake, the inside of the boost pipes and the air temp sensor. While I was under the bonnet I thought I'd take the egr apart to see if it was stuck. In the process of this I found out that the egr wasn't blanked so in theory yes it could have been stuck. So I cleaned it up and it was operating smoothly so reassembled everything. I blanked it when putting it back together with a plate I bought but never used.

Just like before, there was no boost and no power but lots of black smoke out the exhaust when I put my foot down. I disconnected the maf sensor again and boost was back.

Basically I'm confused now. If the egr is blanked and the valve is not sticking why am I still getting that fault code and why is it not running properly? Disconnecting the maf does help but I just don't understand why if the maf is at fault an egr code is coming up?

I plan to sell the car in a month or two and I don't want to throw more money at it, what do people suggest? Replace the maf at a cost of £45~ and hope that helps, or get a new egr valve at almost £100? And is changing an egr just a simple swap or does it have to be programmed or anything?

Getting really annoyed with it now and would really appreciate any help anyone could offer