Citroen Relay - stuttering under acceleration after engine replacement

[Chaplin_Harry123]

Hi all,

I new on here so pls let me know if I miss out any vital info...and thanks for any help in advance. I've not got the VIN number to hand currently but can get hold of it.

My girlfriend & I bought a 2017 Citroen Relay to convert into a campervan & the conversion has been the easy part...we've had a load of issues surrounding injectors & oil loss that ultimately led us to having the engine (replaced with a reconditioned one), turbo, radiator and all of the relevant seals & gaskets replaced by our local garage (the full story is long but if anyone thinks it would help come to a solution then let me know & I'll write it all out). The garage test drove the van a few times before I collected it & all was fine. However when I first drove the van, with a couple of miles of the garage, I noticed what I can best describe as a stuttering under acceleration. It's not consistent as far as I can tell & the acceleration doesn't need to be at all aggressive (say around 2000rpm).

We're getting the following codes:
U1218-81 - built-in systems interface: communication not valid
U1113-87 - ABS/ESP ECU: absense of communication

The air mass sensor has been replaced to no avail.

Otherwise, the van is seemingly working fine. Any bright ideas or cunning ways of narrowing it down?

[Rp0thejester]

Are you changing gears at the point then it starts stuttering?

[Chaplin_Harry123]

No, not changing gears.