I'm not sure if this is of much help to you or not, but when I bought my car (2003 with 95,000 miles on it at the time of purchase) I had the same "issue". It seemed like I had a surge about 40% of the time, mainly when I was driving spirited. After reading everything on here I assumed I'd have to change out my Vanos seals because all the info makes it sounds like it's inevitable that they are bad by that mileage. Well fast forward to today....15,000 miles, a year, and TONS of other issues take care of later and I don't have any "surge" issues any more and I have no plans to dig into the Vanos unless my valve cover springs a leak, and at that point I'll likely do them just because I'm halfway there doing the valve cover anyways.

My point is, with intermittent surge like you have and the car being new to you, you may want to wait a bit and make sure EVERYTHING else is sorted out. Do a couple oil changes with proper oil (you don't "really" know the last owner pout the right oil in and changed it regularly). Drive it like you stole it here and there, and generally get things back up to snuff. Unless the seals get so bad they care causing stalling issues, if they are bad it's not something that MUST be replaced asap. I'd look at your fuel filter, DISA and vacuum leaks first and foremost and go from there. :thumbup:

Just FYI (I'm not saying you need to replace all this) in the first year as far as parts that MAY of helped my surging go away but were replaced for other issues or just for preventative maintenance, I replaced the following...

SAP Hose (Hose connector was busted off)
Both intake boots (Replaced for preventative maintenance)
DISA O-Ring (Replaced for preventative maintenance)
Cleaned MAF (for preventative maintenance)
Lower CCV hose (They were cracked, CCV seems to still be working fine)
Intake and Exhaust sensor (They were OK, replaced for a non related issue)
Plugs (Replaced for preventative maintenance)
Fuel pump/Filter (Pump died, filter was original)


So like I said it's hard to say if your Vanos is bad/going, because all my surging is gone after doing all this other crap, so at least in my case I feel like it must of been caused by one or more of these other components I replaced over the past year.

 

I am confused, wouldn't a "surge" increase RPMs? But you're saying RPMs go down? Unclear about what exactly is happening here.

Does this happen between 2,500 and 2,800 RPMs and completely go away at 3,000 RPMs?

What is the RPM range, engine temp, etc., when this happens?

Any SES or OBD2 trouble codes?

 

The rpms dont have a visible drop, but you can feel a lull in power for a short millisecond then a surge of power as the car continues to accelerate. Its roughly between 2k-3,500rpm.

Temp gauge is at normal (half way between hot and cold.)

 

http://www.e46fanatics.com/forum/showthread.php?t=966614

But before you jump on VANOS seals, you have PLENTY of other things to sort out.

See the first 3 links below in my signature as well.