V50 D2 Engine stutter/hesitation

[Petey80]

Hello all, hope you are well.

Last June I had injector 1 replaced as it failed. Mobile mechanic guy came out and changed it, then had to take it to a specialist to be coded and adapted.

All was well.

Then the cold weather starting setting in the injector started chuffing when cold and stopped when the engine was warmed up.
I assumed the copper washer/seal must be bust so I took off the intake piping and had a look at the area. There was black crud in the area so cleaned it all off.

Had the day off yesterday so got the garage to take a look and as suspected the seal was bust. That was replaced.

Now, the car has developed a stutter/hesitation when putting your foot down at 1600rpm up until about 2k.
There is a little splutter in 4th gear, but 5th and 6th gear is quite violent.
There also seems to be an electrical whirring noise when the car is under load and you're going up through the rev range.

Any ideas?