This is where a lot of JTD and other marque turbo diesel car owners get a little confused.
Yes, the MAP sensor and EGR valve are surely the main culprits to excessive smoke due to carbon build up etc.
But... You have to look further than that and ask yourself, what is causing this build up in the first place?
Two things spring to the mechanical logic process right away.
1. Short, regular journey times, your engine is not getting to optimum running temperature to burn off the carbon build up initially. When a diesel is cold , it naturally runs richer.
Imagine it this way:
You have some lovely, clean alloys fitted to your car. After a week or so they start to accumulate brake dust from the calipers. That's easy, you just clean the brake dust off... What happens to those alloy wheels if you leave the brake dust on for six month or even more?
Layer upon layer of brake dust builds up and then you cant remove it with shot blasting the entire alloy wheel down and restarting again.... Apply that to your exhaust manifold and then you can understand why despite changing/ cleaning these sensors and valves, the car will still produce sooty black smoke.
Using a proprietary product to treat the fuel will work, but only on the latest soft layer that built up recently. You still have the excessive hardened build up that the fresh soot just loves to stick to.
2. Look at the commercial fleet market. Millions of trucks and vans on the roads all with turbo diesel engines and at least 75% of them with EGR valves and MAP sensors... Despite this they don't suffer the same issues as car owners (see initial point 1 for the reason).
Something else apart from longer journeys that they do differently is changing the fuel, oil and air filter far more regularly than a car owner.... On average a commercial van/ lorry is in for service every 5-8 weeks!
Take a leaf out of the commercial fleet user's book and....
Change your driving habits slightly by resisting the temptation to just jump in the car to go to the shop a mile away.
Keep to a constant speed on longer runs to encourage even burn temperature of carbon deposits as this breaks it away gently.
Last but not least, save the money that you waste on fuel additives and over priced performance fuels and simply change your filters a lot more regularly, in particular the fuel filter...
You live and learn...
I once spoke to a friendly Iraqi Kurd who owned a Fiat Marea JTD with 200,000+ miles on the clock when I served over there.... Now I knew the quality of the fuel in Iraq was simply typically an old guy with a 100 gallon oil drum, a length of hose pipe and a dirty rag by the roadside... Despite this his JTD was running perfectly without issues.... He had to do a round trip of 250+ miles per day and changed his filters every few weeks due to the dusty, sandy conditions...
Now if he could keep a JTD running like that, why do UK users insist on blaming everything else but????
I leave it to you guys to decide what you should spend your hard earned money on