Stuttering engine then stall

I was very pleased to get an Audi 1.9 TDI as I have always wanted one and got this car recently as we don't have a lot of money. But then issues started to arise. Recent work done had been vacuum valve and crank sensor replaced.


First, discovered a flooded plenum chamber and water in relays under ECU which caused limp mode plus soaked carpets inside drivers and rear passenger behind driver side. Cleared blockage and dried out relays and all appeared good.


Two days later I got check engine light light and code P0230 but car still ran fine.


Three days after this, as I was arriving home from a long drive on motorway the car started to stutter at about 10 mph and then when I parked up and started it again, rpm was jumping up and down in idle and stalling, then it cranked but wouldn't start. I then replaced relay 219 under ECU as it appeared to have corrosion on the contacts. Cleaned electric contacts on relay holder. All other relays and fuses appear to be fine. Car took a little while to crank but once it did all appeared good again. 


Drove for another two days with no issue, then today while driving, engine started to shudder and then stalled at 25 mph losing power steering and red battery light on dash. Took about three minutes of cranking with foot on gas pedal to get engine started again. This happened three more times on way home but did make it back. No codes have come up at this point. Car starts at moment but I'm expecting that it will continue to do the same as it has been.


I have been advised to replace diesel fuel filter as first port of call but I'm worried I'm just going to be throwing money at it. Does anyone have any idea of the likely reasons behind this happening? I'm a novice mechanic i.E. Brake pad and filter changes etc, I just hope someone has had the same symptoms and has been able to fix.


Thanks in advance.