New guy introducing himself; also have a question.
 

Hey everyone, first time posting on PP but I have been lurking around for a little while. Seems like people here seem to know their stuff and are pretty friendly so I figured I'd join. My "new" car is a 98 M3 as seen below. She is very clean and I intend to keep here that way. :) I love driving the car as it has a very linear and torquey power curve, great balance and brakes, and, IMHO, is a genuinely fine car. But, I suppose that I am preaching to the choir. Upgrades include a Supersprint catback, Koni shocks, and some other non-performance knick knacks.

One of the exterior, one of inside:
http://i185.photobucket.com/albums/x...r/DSCN0249.jpg

http://i185.photobucket.com/albums/x...r/DSCN0248.jpg

However, I do have a question. The car was neurotically maintained by the previous owner, but there were a couple of small things that needed to be replaced. When I bought the car, it had almost 100k miles on it and, as though they were on meant to do so, the O2 sensors failed just as I cracked the century mark. However, preceding the replacement of these sensors, I noticed that when I would go to full throttle, going from first into full throttle second gear, the car would hesitate. When the CEL came on for the O2 sensors, I had earlier that day had my first real experience with this hesitation. When they diagnosed the O2 sensors as being bad, it seemed odd that the two would be linked but I was willing to be patient. The sensors were replaced, the CEL went away, and I continued to drive the car normally. I think this is a good time to mention that I do not drive the car like a lunatic and only occasionally use full throttle. However, the hesitation is still there. I want to say that it occurs 1 in every 8 or 9 full throttle 2nd gear applications. I believe that it is a cam sensor or something of that nature because when I go from 1st to 2nd, it will hesitate for what seems to be about a second and a half, and eventually give me full power. My thinking is that the sensor can't position the cam and once it is able to do so, it allows me to go full power again. I can actually feel it slowly giving me the full power back as this is not an ON/OFF thing.

The only other thing that I could be associated with the same problem would be a very very slight bucking at rpm's ~1200 and below. I don't believe that to be normal as my previous car didn't have that problem. I am not sure if they are linked.

If anyone could give me a potential diagnosis, that would be awesome. The car was scanned when I replaced the O2 sensors and I believe the guy said that nothing else came up...it seems like we have a hidden gremblin in there. This also confuses me as I thought that any sort of misfire would be recorded by the computer and show up during a scan. I am very sorry for the lengthy explanation but I felt it neccessary to give everyone all the details. I'm looking forward both to hearing from you guys and being a part of the community. SmileWavy

It seems unlikely that two O2 sensors would go out at one time. Did the O2 replacement have any effect on the problem?

This problem is going to be very hard to figure out. I could be VANOS solenoid, fuel filter, fuel press regulator, spark plug, coil, fuel injector, vacuum line, just to name a few.

A cam or crank position sensor should throw a code.

Great car though. Mine's been down more than up the last two months and I miss it. :(

Jeron, thanks very much for the response. First of all, sorry to hear about your car. Hopefully whatever is ailing it will be resolved; best of luck on that front.

Other than causing the CEL to go out, replacing the O2 sensors had no real effect on the way the car drove. I should have also mentioned that I switched back to the OEM spark plugs right after I got the car (NGK's) because I wasn't too thrilled that the previous owner was running Bosch Platnums, so those should be good to go.

I suppose that the best thing to do what be to go through the little checklist you mentioned and see if any of those hits the problem on the head. Again, all help and insight is very much appreciated so if you've got an opinion I'd be more than happy to listen. :)

Sounds like the typical coil failure! Best checked in a dark garage with the coil/plug cover removed so you can see any arching. Coils (6) seem to have a life span of about 60K then best replaced. Good time to do new plugs too.

Okay, just a quick update for everyone. I checked the plugs and the coilpacks and both seem to be in good condition. My new theory is that the ASC, which was turned on during all of these runs, was adjusting for any wheelspin that took place when I upshifted. I think that this would explain the lack of a CEL, the fact that it only happens going into 2nd gear and demanding full power, and the fact that this hesitation happened multiple times when I was driving through some sprinkler-water runoff. Furthermore, I had the hesitation happen to me once two days ago and, sure enough, I left the ASC on for some reason. I also lifted when it began to hesitate and then went back to full power without trouble. Other than that, the last few days have been ASC-less and I have yet to have this problem again. I'll keep everyone updated if it happens again while the ASC is off, but I believe that I've pinpointed it. Jeron and islandmanpa, I appreciate for your input. I know how difficult it can be to diagnose someone else's problem with limited information and not experiencing it first hand. Many thanks.

Don't want to state the obvious but going from 1st to 2nd at full throttle do you pass the rev limiter threshold? This will cause hesitation. My wife did the same thing from 1st to 2nd on a 325iS and didn't realize that she was hitting 6500 - 7000 rpm's. She does this regularly on my Alfa Milano which has a higher rev limiter. Just something simple to check out before you chase the gremlins.

The ASC light will flash while it is activated, but you pretty much have to be looking at it because it does not continue to flash once it becomes inactive.

bimmertomnv, I am absolutely positive I am not hitting the limiter threshold. I have done that before and I know what that feels like. What I was describing is like that, but more more abrupt. I was again out and about tonight playing with the ASC, turning it on and off and, based on what I experience, I am not certain the two are correlated. Thanks for mentioning that though. That would have been a good comparison in the description in my OP! Again, I appreciate the feedback, especially for a new member.