I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked
I would not expect that the timing being off would casue an intermittent issue.
I would suspect possibly the airflow sensor as the culprit, or potentially a vanos issue.
as a next step, you could try drivinig with the airflow sensor unhooked.
I would also consider a software update at a bmw main dealer and potentially new cam and crank sensors as there have been some issues with them
I agree that a timinig job would not be a good investment given the value of the vehicle.
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.
Thanks - I do have a couple of follow on questions.
Firstly, where do I find the airflow sensor, and how do I unhook it?And if it is unhooked - what does this actually do for the engine?
Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you.
the airlflow sensor is on the intake side of the engine near the air filter box per the images below. you simply disconnect the electrical connector. If you are not familiar with this type of thing then you should consider having a professional do it.
unhooking it makes the engine use default air/fuel mixture values. if the sensor is faulty, running with it unhooked will cause the issues to cease. You may also want to have the intake checked for leaks and the crankcase ventilation system tested, although these are less likely to cause what you have described.
part #1 here: http://www.realoem.com/bmw/diagrams/u/x/114.png
Thanks very much for that.
The second question is what is the vanos?
If you could return some diagrams and images as well again, that would be helpful.
the vanos is a variable timing unit
it cannot be worked on at home, it 100% requires a professional and special tools
Oh I see - so fixing vanos would be part of that prohibitively expensive timing repair job then.
I just read up about how the vanos seals failure can cause my symptoms. But again I would expect consistent problems now following a gradual deterioration in performance.
Do you think vanos is likely or unlikely in my case, given the overnight recovery, and the fact that no specifically vanos fault codes were there?
I think it is unlikely. as the question has been answered, please kindly CLICK ON a positive ratinig. thank you