I was having exactly the same problem with my 2014 Seat Toledo 1.2 TSi and I found this thread by searching the web for these symptoms. Thankfully I had only tried replacing one other part earlier this week, when I found this thread, so I immediately looked at my coilpack and leads. In taking the first lead off the coilpack, I found the end of the lead was stuck on the pack, because of corrosion. I also had corrosion on at least one other lead where it plugs onto the pack. So I replaced the leads and the coilpack and this solved my problem. It is quite difficult to describe the symptoms to someone, as seen from this thread. I would say that while anywhere between about 20mph and about 40mph, and while accelerating quite hard in 2nd or 3rd gear, and with the RPM from about 2000 to 3000, there would be a sudden, significant drop in power, followed by it immediately coming back, and then dropping again and coming back again - multiple times within one second - hence someone calling it 'juddering' - so much that the passengers could feel themselves being shaken backwards and forwards. I really pushed it hard one time to try to work out what was going on, and it caused a load of faults and warnings to appear on the display, and it to go into limp mode. The problem manifested badly one day last week, but looking back on the last few months, I've now realised that it had started to happen, but much less severely, a few months ago. So, this may help someone: in my experience, the first sign of it back then, was that I would pull out onto a 60mph road from stopped, accelerate quite hard, and everything would be normal until there was what I thought of as a 'dead spot', probably while in 3rd. It then immediately picked up again. I noticed this quite often in that same place each time after leaving work. I put it down to something to do with the turbo (not knowing much about how they work), or more likely, a worn/dirty region on a potentiometer - either the accelerator, or the throttle body position feedback sensor (having already had very similar symptoms due to a broken internal connection to its PCB a few months ago). Before I found this thread, I checked the accelerator pot, which was fine, and I replaced the throttle body with a second hand one. So thanks everyone for your input in 2018!