Don't know if this makes any difference, but I'll give you my idle story.
I recently picked up 318is and have driven it for about 3 weeks. When I started it up when it's cold, it would idle for about 20 seconds and then just die and catch itself and pick back up, if I drove it while it was cold, coming off a stoplight, it would stumble and buck hard, sometimes when it did it, I would see the CEL flash. As soon as it warms up, it went away. I usually do PM on my new vehicles, so I started out with the fuel filter and air filter. When I changed the fuel filter out, I found that the internal element had somehow broken loose and was just jingling inside. Swapped it out and the car hasn't stumbled on cold start idles since, but it did buck on me one time when it was cold while I was driving.
I'm still having small idle issues, nothing major like everyone else though.
1. Cold start idle is low, about 800-900, as the engine gets warmer, the idle gets higher, when the engine is fully warm, it idles at 1000-1050.
2. When you stomp the gas when it's sitting, it has a slight hesistation, but then picks up.
3. If you leave a stoplight and roll into hard, past 50% throttle, it kind of bucks and stumbles slightly.
Doesn't seem to be the same problems everyone else is having, but none the less, still an M42 problem.
Also, just a few things I've learned, when a cat's clogged, it usually it hotter then normal, I don't know exactly what the normal temp of a cat is a optimum effeciency, but I've heard of clogged cats glowing from the heat.
Also, I've had friends that work in shops that have had sensor problems and noticed that when certain sensors heat up from the engine, they short internally, causing irratic signals.
Just a few things to think about
