I have 2002 Jetta TDI with 147000kms. I am a heavy duty mechanic, so I know diesels and electronic controls, but am not exactly sure how volkswagen does things. Just recently me and the wife were on a 450 km trip home and I passed a guy on the highway and then all of a sudden I lost power. I am assuming this is some sort of limp mode??? Will it throw a code if it goes into limp mode? The low power is intermittent, I have been driving the car for 2 days and it hasn't done it again yet but when the wife has been driving it for the last two weeks it has been off and on. Also, when revving it up in neutral no load, it runs OK from idle to about 2000rpm and then from 2000 to about 3600-3800 it runs rough and smokes white and then after that it starts running fine again up to high idle ( 5g's).When we got home I did some work to it. Changed the fuel filter (CAT2). Checked all fuel lines, and fittings on top of the filter head etc, even ran car from a jerry can to see if it was sucking air somewhere. Noticed the clear line from the filter head to the injection pump does have quite a bit of air in it which is never good for a diesel and doesn't seem right to me but I talked to another guy that had a 99 tdi and he said his always had air in the clear line so I am not sure if this would be part of the problem. I also tried temporarily replacing that clear line with a new fuel line to see if it was sucking in air from the fitting that changes it from the rubber black hose to the clear tube.Still didn't run OK. I have VAG-COM and there are no codes whatsoever. I did the timing belt in january and set the injection pump timing properly with VAG-COM (ran ok since january up until two weeks ago). I rechecked the injection pump timing and it is still good. I have the Bentley manual but it only gives me troubleshooting steps for codes and repair procedures it doesnt explain how the electronic systems work and how the fuel pump is controlled etcetc. I did a couple datalogs and the one major thing that I have noticed is that the start of injection looks good for at idle when you actually set the IP timing after you do a timing belt (it only takes into consideration timing at idle). But when revving it up the timing doesnt look right, at certain rpm's it actually goes into a degree or so ATDC which does not seem right to me at all. The higher the rpms are the more advanced your timing should get. now once the car starts to run properly again at about 3600 rpm is when you see the timing coming in and maxes out at about 16 degrees BTDC at high idle. If I knew someone else with a TDI I would plug into theirs and check the timing out but I don't so I can't. I believe I have a timing issue (would make sense with symptoms of rough running and white smoke). What I don't know is what sensors the ecm takes into consideration when advancing and retarding the IP timing is it strictly RPM or would it be others as well? Could a sensor fail within programmed parameters and not throw a code but would affect the IP timing? Could it not be electronic at all and maybe the actuator for the advance cam plate or whatever be malfunctioning and not setting a code. Or could something be hanging up in the pump? These are the kinds of questions that my Bentley manual doesn't answer. I think I am on the right track but I need a VW GURU! to help. I have the datalog but don't know how to attach it to this post so if someone wants to see it I would gladly if you could tell me how to post it. Any help would be greatly appreciated! If you need anymore info I will gladly get it for you. Thanks!