not exactly a new issue here I see but I would like to elaborate slightly on the information other people with the same/similar problem have given. I have a 2005 mk2 focus 2.0 diesel estate, I bought it privately from a guy in Bristol 9 months ago. I paid £1900 pounds which seemed a great deal to me for what I was getting but gave it a good look over and drive and all seemed fine. I drove it the 120 miles home, no problem and for around three months it drove like an absolute dream. Then one day without warning it completely lost power, it was like driving a 0.8.
Ever since then it has done this every 3-4 days. There is no bang, and no black smoke but the lack if power is massive, putting your foot down hard doesn't make it rev any higher and if you keep it down and try to force it, it judders. The engine management light has come on twice over 6 months when it has happened but that's nothing in the 50-100 times it's happened. Now,the strangest thing I find in all this which I couldn't seem to find in other discussion's apart from one, is that turning the car off and then back on instantly fixes it-obviously until it happens again. I don't know much about cars but this to me suggests that there isn't a major mechanical fault as, if there was, the car wouldn't EVER run properly. That said, even when it is at full power these days it isn't as smooth as it was and always seems to be threatening to go again. So this has me thinking it is either a dodgy sensor or something is causing an incorrect mix of air/fuel. Most people with similar problem are quoting either map sensor, egr valve or dpf. To me the egr valve makes sense, especially if the previous owner had it cleaned as apparently this can give it a short term fix.
The other thing I forgot to mention is that it definitely happens a lot less if you keep the fuel topped up, and this has my local mechanic convinced that it's either the fuel filter or a weak fuel pump. The problem seems fairly common across focus and mondeo diesel's but there doesn't seem to be a definitive YES-this is the problem and this is how you fix it, so I was hoping people who have managed to get their cars running properly again could all put how they did it on here. I have registered the problem with Which as they are trying to put more pressure on car recalls and if this is a common problem it's not on. The power has gone on the motorway a couple of times and it's scary, I wouldn't want to have kids or family in the car.
In the meantime the car is having a new fuel filter in 6 days so I will post the result regardless of whether it works or not.
Sorry to ramble, any information would be massively appreciated!