I bought myself a 2007 Ford Focus 1.6 TDCi just over a month ago now with 94k miles on the clock, and I seem to be having a few problems with it!
One day I turned the car on to drive to work and the revs were dipping at idle and when trying to move off I stalled. When I managed to get going, the car was jerking all over the place, revs were going crazy. I took it to a garage which was recommended to me and they disconnected the mass airflow sensor and, although the engine warning light was on and there was a slight loss of power, the car ran fine. After a week I went back to the garage and they replaced the sensor but then the jerking problem came back about half an hour later, so I got my sensor put back to the original one and went to a Ford Specialist garage who said that there was an air leak which I got fixed and they hooked up the airflow sensor again and everything was then fine. They also said there was a fault on the DPF but a good drive in the lower gears would fix it.
After all of this, whilst driving around I noticed that the car would sometimes slowly feel like it was losing power over the period of about 3-4 seconds, then would judder every so slightly, but I thought nothing of it apart from that it could be the DPF. I was told to take it down the motorway for a good blast, but being a learner and driving around with my Dad, I couldn't do this! So instead I drove around some dual carriageways in 4th gear at 70mph for a good 30-40 minutes. I also started driving in 3rd at 30mph instead of 4th.
The problem seemed to get better until Thursday (a day before my driving test!) when the car went mental again and was jerking all over this place, this time with a knocking noise if I managed to get the revs to about 1800rpm. Black smoke was coming out of the exhaust also. I managed to drive it around the block very carefully and the jerking went away along with all the smoke, so I went to take it for another blast down the dual carriageways, however after about 5 minutes a red light game on with "ENGINE SYSTEMS FAULT", so I pulled over as soon as I could and turned the engine off. 5 minutes later I turned the engine back on to drive home, the error was still showing, there wasn't any jerking but the car had NO power. Moving away from junctions was a very long process and I was at this point getting worried that my turbo had failed or something, but after reading about it, it seemed to have been "limp mode" (which I don't know much about!).
I took it to the specialist garage again and they said that my DPF was completely clogged up and they were unable to get the engine above 3000rpm to regenerate it. They suggested having it removed but some quick research showed that it is illegal and my MOT would fail Feb 2014 onwards. They told me that the DPF does cause a lot of people problems but usually only becomes a real issue if you drive around town too much, and/or there is an underlying problem to which they had found some contamination of the mass airflow sensor with oil or something (he didn't go into much detail, they're going to look into it more tomorrow)
I was just wondering whether anyone had any ideas/advice on this as I'm unsure what to do. My car is still under warranty, but the private dealer I bought it from wants to take it to his garage for a checkup, and I'm worried that he's just going to apply some temporary fixes so he can get out of the 3 month warranty.