Sorry for the massive delay, had a busy few days but a lot has happened.
Getting the car started:
After removing the quick connector on the fuel line in the engine bay, no fuel was coming through, despite fuel coming out of the pump. I attached a piece of transparent hose to the fuel outlet on the pump to see if there were any issues. Lo and behold, there wasn't enough fuel pressure to get it through the hose. I knew this was an issue with o-ring placement on the pump, but I just couldn't get it tight. Eventually, I tried placing two o-rings in there (old and new), so the bottom one pushed the upper one into the socket. I could immediately tell it was in properly as it was difficult to remove again. The next day, I refitted the filter and it started first time 😁. I've attached a picture for clarity.
After driving around a bit today, I noticed the stuttering issue was annoyingly still present. After a while I got fed up, so when it started juddering, I just held the throttle at the point that was causing it. However, after holding it for ~ 5 seconds, an engine warning came on as well as a VSA 😬. Luckily, my mate was in the car with me, who has an OBD2 reader, so I carefully drove to his house to pick it up. The code
was as follows "P0339: Crankshaft Position sensor A circuit intermittent."
The VSA warning wasn't present after restarting the car, so I presume it was just because of the juddering.
We cleared the code and looked at the full system information. I noticed that the EGR Error percentage was at 99.2%, indicating that it's virtually dead. We took it for a spin while using the code reader to monitor the throttle position, engine load and fuel system.
When the stutter occurs, the engine load jumps to 100% regardless of what it was previously, with throttle position fluctuating slightly (although this may be the car juddering causing the throttle to physically push against my foot). The EGR error percentage remained at 99.2% for the whole time.
I also managed to keep the car stuttering for ~ 5 seconds and the engine warning light came on again. The same code (P0339) was present.
Based on the fact that the stutter only occurs when under load, I think that what happens is that due to the EGR valve not working correctly, when the ECU is attempting to fire it and hence expecting the extra gasses, when the gasses aren't present the engine spikes to 100% load to compensate, causing the judder. This would also line up with the fact that throttle response in the leadup to a judder feels extremely lacking.
I reckon the engine warning code is thrown up as due to the harsh juddering (feels almost like stalling a diesel, but for 5 seconds straight), there may be a loose connection on the sensor, momentarily causing a voltage fluctuation.
My next move would be to purchase a new EGR valve, but seeing as it's £70 for a new one, I thought I'd consult you guys before doing it, as I don't want to mindlessly throw money at it, or ignore issues that may be more severe than I realise (i.e. the crankshaft sensor).
hopefully you find this useful, and if you've got any more questions feel free to shoot them my way, I'm happy to help 😁.