[SSW]

So, I was driving around in my 2008 E90 today, stopping at various locations, when the car unexpectedly started to misfire and vibrate around 3k rpm in D and DS modes. The "Service Engine Soon" idiot light also came on at the same time. I switched to Manual Mode and increased the revs a constant 3-5k rpm in various gears and pushed the revs to 5-7k a couple of times, as well, in M, DS and D mode and eventually the vibration and misfiring and the service light went away.

So, what do y'all think is the cause of this and is this, as I suspect, just a precursor of a need for a walnut blast cleaning and spark plug/coil change?

Update:

Took the car out for another short drive after installing a set of 12/15mm VRSF spacers on the car and the vibration and "Service Engine Soon" light came back on. Did the same run thru the revs routine as before and the vibration went away but the light stayed on.

Quickly figured out that "Service Engine Soon" is BMW's way of saying "Check Engine." So, I pulled out my Cobb AP3 and hooked it up to find out what the CEL codes were and this is what I got:

P29CD -- Misfire Cyl 1
P2F81 -- ??
P2F83 -- ??

Anyone know what these codes mean? The Bentley manual confirmed the definition of P29CD but there were no entries for P2F81 or P2F83.

Lots of discussion in various threads about P29CD but nothing on P2F81 or P2F83. Cleared the codes w/the Cobb AP3 . Will re-read the codes if the problem returns to see if it's the same. I guessing the the problem is related to at least 1 or more of the following: plugs, coils and injectors. If so, I hope the problem is limited to Cylinder 1 only. The car is going into a shop to install Koni FSDs next week and, if the problem continues, I'll ask them to check out the problem as well.

Was planning on doing the walnut blasting cleaning and spark plug change at 100k miles (currently at 88k) but this problem may push up the schedule for doing that.

Update 03/24/14:

Have to admit that I was a little gun shy starting up the car today but I had to run some errands and wanted to see if I the vibration/misfire would come right back or not. Just took a little 10 mile drive but made it thru w/o any more CELs today. Admittedly, I took it pretty easy on the throttle so as not to aggravate the engine but that's a good sign. Still going to take it in later this week for a plug/coil replacement and the walnut blast cleaning anyway.

Update 03/26/14:

Got another CEL today -- P29CD (Cylinder #1 Misfire) but not the other codes. Did the rev/gear run thru as before and the CEL went out but the DTC came up when I hooked up my Cobb AP3 to read it. Hopefully, the plug/coil change and walnut blasting that I'm getting done tomorrow will fix this.

Updated 03/27/14:

Got another misfire CEL today on the way to Master Automotive in San Jose where they are going to a walnut blast cleaning of the intake valves and install a new set of plugs and coils. The misfiring this morning was actually much worst than before but it did resolve it self after I ran the car through the gears at high rpm again.

As noted below, the cleaning and plug/coil replacement seems to have solved the problem; the car runs smoother and there were no misfires on the way home after the work was completed.

[SSW]

So, no one knows what the DTC Codes P2F81 and P2F83 mean?

Well on the assumption that it MAY be a bad coil AND, since the spark plugs were last changed at 50k miles and are "due" to be changed at 90k miles which is only 2k miles away, I just ordered a set of plugs and coils from ECS to be installed at the same time as I get the walnut blasting of the intakes done at a local shop.

Hopefully, this'll solve the misfire problem. If not, I'll at least have ruled out the plugs, coils and dirty intakes as the cause, which probably only leaves an injector as the source. We'll see . . .

[SSW]

Just got back from San Jose where Master Automotive did the walnut blasting of the intakes and replaced the plugs and coils in my 2008 335i.

After all the work was finished, I drove the car 55 miles back to my home and it the car ran very smoothly with no more misfires or CELS . I wouldn't say the car is more powerful, but it runs noticeably smoother than before. Just step on the gas and WHAM! the car accelerates effortlessly. It's pretty amazing. So, I'm very happy.

You can find a more detailed report of the work done here.