I saw this thread and thought I would respond.
I have had a vanos failure on my car. So I thought I would share what happened.
Firstly car Stats : 2006 M3 with approx 28k miles at time of incident. No modifications to car.
My wife was driving the car and said it was surging on the freeway when it was at a constant speed on the freeway (approx 75mph) the car would just surge like a misfire. I said sure sure I will take a look at it thinking it was something she was doing. Sure enough driving not under acceleration but constant speed the car was misfiring. So I took into the dealer.
It was 1 week prior to christmas so that didnt help with getting parts in and the car was in the shop for a total of 8 weeks. Luckily the dealer provided a rental car.
So here is the story of the problem.
Dealer rings: We have connected up and you are misfiring on all cyclinders but we are still looking into it.
Later that day: We were checking things out and it just fixed itself. But we will keep the car fo rthe rest of the day to see if it comes back. Sure enough it came back.
1 day later: Our staff have no idea what the problem is so east coast engineers asked us to run some diag tests.
2 days Later: We think it is the vanos solenoid playing up and will ship in a new one.
4 days Later (after christmas) : That didnt fix it. RUnning more tests by east coast engineers. We think it might be the vanos system, ordering a new one and will let you know.
6 more days later: We have the new vanos and installed it and that didnt fix it. We are unsure. More tests and talking to east coast.
days later: I get a call, the timing is out, did you change it. My response, no you are the only guys that have worked on the car so unless you changed it I dont know. Ok we will fix it. (At this point I am thinking why didnt you check timing at day 1 when you knew it was a misfire? Surely that is fault finding 101)
more days later: Timing didnt fix it we think it is the gears that attach to the vanos and the cam is warping under stress at high speeds. (I think gears warping that is a stretch but whatever keep trying.)
more days later: We found the problem. 2 bolts were cracked that attack the vanos gear to the cam shafts. There is apparently only 3 that hold it on. So it was moving around all over the place.
I get the car back and drive it home and it plays up agains.
I take it back and there was a problem with the throttlebody as well that they fixed.
The best thing they covered it all under warranty. So I got all the new system and everything with no cost.
But overall if vanos is playing up it will feel like a misfire and when diagnosed it will be on all cyclinders.