Failed mot on emissions.

[rodders 204]

So, I bought my 1.9tdi 130 high line last November. Just took it for thr first mot in my name, but it failed on the emissions. Badly!.
The previous owner was a 70yr old lady, and it would seem that she drove only in town, and in 6th gear. I don't think she made the car work hard since she bought it 8 years ago!
I have now inherited this problem. The emission testers screen showed 5.4. That was after I had poured x2 bottles of fuel additive in the tank over the last 6 months, and have just fitted a new air filter to help also. Also, I have been deliberately driving in a lower gear than required to make the engine rev higher. I have also just fitted a new battery, as the glow plug display on start up, was taking longer than usual to turn off.
The car runs spot on. Pulls like a train in all gears, uphill, no shaking, no vibrations, nothing. Runs great. Only one thing I have noticed bad, when I drove my van behind my wife in the car, as she put her foot down, there is a puff of smoke from the exhaust that lasts a couple of seconds only, then clears. I have checked the EGR valve. This was replaced just before I bought the car, and is working fine. I'm thinking that the injectors need a clean {I would put it into a Bosch engineer, who cleans injectors \fuel systems locally then checks emissions before releasing the car back to me}.
Does this sound like the cause, or can anyone give advice please.