Hi everyone, this is my first time posting on this forum so bear with me please.

I own a 2009 Ibiza with the BLS 1.9 liter engine. A month ago I changed 3 out of the 4 injectors as they were knocking pretty bad and I had trouble starting the car. All of them were tested and the technician said that the fourth one is ok.

Immediately afterwards, the MAP and MAF sensors had to be replaced as it started to have missfires so bad you couldn't even leave the parking spot. By immediately I mean right after putting everything back together and starting it for the first time.

Also immediately afterwards, the car developed strong rythmic vibrations under acceleration in 4th and 5th gears at around 2000rpm. Ever since that started happening I've struggled to find out why it happens. Yesterday I got hold of a VCDS tester and it showed that injector nr 4 was sitting at around 1.4 correction. Two weeks ago, on a Delphi tester everything looked really well and no injector had high deviation correction values, injector 4 sitting at a comfy 0.20.
At the same time I noticed that the underside of the tandem pump is wet and black. I suppose it is leaking diesel, even though I couldn't identify the fluid by smell.

My question is: could a dying tandem pump cause the strong vibrations? Could it also cause the high correction on injector 4?

Thanks and sorry for the long post!