First of all, i'm not from UK but i've been reading your forum for quite some time and it seems like there's lots of expertise here. I have a big problem with my S50B30 engine M3 (-93) and I thought maybe someone here could have some ideas..
The problem doesn't appear always, it was off for like 2 months after the main dealer "cleaned some terminals" and such but now it has started appearing again. The symptoms are that idle drops to 500-600 rpm and car shakes and splutters. If given some gas the shaking goes away but there's still some spluttering. When driving it seems perfectly okay when not in idle.
It's been to the main dealer for 4 times now because of the same problem and I've spent a lot of money changing this and that but they really can't figure out what is causing it. If i let the car idle, it might do it for 5 minutes and then suddenly start idling perfectly again. The only thing the mechanic at the dealership could figure out was that it could be something to do with the VANOS being in improper position and thus causing what appears like lost compression(intake valves open too much). Compression test showed all cylinders good.
What I would like to know is how the VANOS works on the 3.0L? Is it a three stage system? So that it is same in idle and high range and different in middle rpms? How does it change the timing in middle, to which direction?
And should it be "de-energized" on idle? So if one would take off the control plug of the VANOS unit, it should idle perfectly and then have problems on the middle rpms when it should be activated? Haven't had the guts to try this yet, so is it safe and a reasonable idea to try?
Could it be an ECU problem? I'm trying to find a salvaged ECU from a similar car to try. Does the main ECU control the VANOS or is there an another one?
Thank you for any possible ideas regarding this! It's been such a pain in the ass for so many months and I haven't really had the chance to enjoy the M at all :(
- Teddie W