Berlingo Kangarooing / stumbling / juddering

[Garf89]

Hi All,
I really hope somebody can shed some light on an issue my van has. It's been going on around 18 months (15k) miles approx.
The van is fine 80% of the time, but the more eco you drive it the more frequent the juddering becomes. I've spent over £1700 on it so far and it's still not fixed it.
The issue mostly occurs in 3rd/4th gear between 1500-1900 rpm, the revs dance up and down, it shakes the van so much things inside rattle and it throws tons of black smoke out...
The first repair was the egr deleted, dpf delete & adblue delete. The garage said it had a lump of coal inside it and couldn't believe it actually ran... Next time I drove it I went for a run in it and the problem was still there. I rebooked it back in, had a full service whilst in.
I have a scanner and the only code it ever threw for me was p0426 - relating to the cat sensors.
Back in the garage he said it had a doser error code - opened it up and the flap was stiff... Bingo we thought, open it up, delete it out of the software and it'll be fixed... Whilst in we also changed an injector that was wet on it's top just to be sure it wasn't 2 faults.
Just done over 500 miles to Wales and back for a few days camping... First 250 miles she ran sweet, better than ever... Until captain kangaroo arrived again. Coming home last night I was down to second gear 1000rpm 10mph trying to nurse it through the problem.
Could it be a boost leak/sensor?
Maf/o² sensor?
Sensor in the cat?
We thought it triggered the cat sensor due to the coal hence that's not been looked into...
I'm fairly handy myself but I've no fancy garage type of computer. I can't afford to waste anymore money on it as I'm getting married shortly...
Thanks for reading...! Much appreciated,
Adam

[GiveMeABreak]

Well whoever undertook the EGR / DPF / SCR system deletions has made your vehicle illegal to use on the roads and your insurance is probably invalid as a result of your car no longer meeting the standards for which it was certificated. We don't condone any emissions crippling on this forum (please read the AUP you signed up to), so you should expect issues if you have made this choice.

[xantia_v6]

You might want to check out the recent Hubnut videos:

and

I cannot vouch for the accuracy of anything on that channel, but he thinks that he fixed a problem.

[Rp0thejester]

My first thought is a faulty turbo, I had a similar issue with a van I was driving, turbo kicked in and out and it was up and down the revs

[Peter Palmer]

Try the crank sensor.

[Garf89]

Cheers.
I'm going to order a Haynes manual and get the spanners out. I'm thinking it's possibly the maf sensor, lambda sensor or the cat is shot. It's down on power all the time now, around 80% of what it used to be at a guess. The map is as clean as it can be but it's rolling coal so it's definitely not getting enough air or breathing right. I've booked it in for a smoke test to test for any turbo, intercooler or hose leaks. I'm time poor hence I've not had a go at fixing it myself but it seems I've no choice as the diagnostics never return any fault codes which I'm amazed at as my previous cars were all too happy to throw a code if it rained a little too much...
Cheers for the feedback, any ideas are appreciated!