[alex2364]

So I have a stock 2009 335i N54 with 42k miles. For the past 6 months I've noticed after a cold start, during idle, I can feel my driver's seat shake and my rpm will jump between 900-700 rpm for ~30 seconds. After I start driving, everything is normal. Four months ago I brought it to the dealer and they found no codes. They said they couldn't find anything wrong with it, but I doubt they did anything more than just pull code and tested my startup a few times.

I searched on here and some people other similar issues said it's cause of carbon buildup. Could it be anything else? Also, my warranty expired 2 months ago, but since I brought the problem to their attention before it expired, do you think the dealer will cover it?

[DASHOCKER]

is this happening after the cold start cycle when the car purrs through both tail pipes?

[Wheezy C]

Mine does the same and its only when the engine is cold. ('07 335i 42k miles) If the engine is warm enough to register temps then there is no issue. This just started recently after a year of normal starts. Only mods are DCI and "golf tee" mod. One of my co-workers had the same issue with his 335i and said it was carbon build up and I just needed to run it a little harder... I definitely run the car hard with redline shifts at least once a day. No change.

[pgaplayerless]

RPM surges on warm up are nothing to concern yourself about.

[Overspooled]

happened to me where the cold start was getting pretty rough and the dealer noticed a faulty injector

[Wheezy C]

Update... Ironically after posting I got a check engine light once the idle started chugging down to about 300 rpm. Dealer appt Tuesday.

[wwc310]

Originally Posted by Wheezy C

Update... Ironically after posting I got a check engine light once the idle started chugging down to about 300 rpm. Dealer appt Tuesday.

just had the same issue. dealer couldnt replicate the problem but i took a video of my rpm gauge. they replaced the HPFP and reflashed the car.

[jeffro535]

Ok, mine was doing something similar, but without the RPM drop, and would occasionally throw misfire codes. Very long story short: after changing the HPFP x2 the LPFP, spark plugs, injectors, complete software update, and about two weeks of sensor output analysis the dealer FINALLY changed the vanos solenoids. All good now.

[pgaplayerless]

Originally Posted by Wheezy C

Update... Ironically after posting I got a check engine light once the idle started chugging down to about 300 rpm. Dealer appt Tuesday.

Not THAT is not normal

[Lifted07Duramax]

In for the fix

[Blcoffee]

I have pretty much the same problem

Did your engine start kind of weak once in a while as well like taking 0.3sec slower to start ?! Because im experiencing this as well.

[Some Asian Guy]

I also had a rough start issue a couple months ago. It was very slight, and coming from a highly modified Subaru, I almost didn't notice it. I mentioned it to my service advisor when I had some AC work done, and he said he'd check it out. The receipt that I got said that one or more injectors were leaking, and they ended up replacing ALL the injectors under warranty.

[Wheezy C]

I got my car back today from the dealer. I had misfire codes 29cc, 29cd, 29ce and 29cf. One of my injectors was stuck open fouling the cylinder and the others in bank 1 were compensating. All injectors in bank 1 were changed and the problem is solved. It runs so much better. Thank goodness for warranties.

[alex2364]

Just to give everyone an update, I had my spark plugs replaced today and it seems like my idle is much smoother. I'll keep an eye on it next few days.

[Lifted07Duramax]

Originally Posted by alex2364

Just to give everyone an update, I had my spark plugs replaced today and it seems like my idle is much smoother. I'll keep an eye on it next few days.

Get your valves cleaned

[fazman]

Originally Posted by jeffro535

Ok, mine was doing something similar, but without the RPM drop, and would occasionally throw misfire codes. Very long story short: after changing the HPFP x2 the LPFP, spark plugs, injectors, complete software update, and about two weeks of sensor output analysis the dealer FINALLY changed the vanos solenoids. All good now.

Vanos cleaning seems to be something that they should do at the same time as a carbon blast (they don't currently... But that would be an awesome indy if they didi it).

[iturbo_bmw]

I was having the same cold start issues. I just got the walnut blasting done yesterday and this morning my cold start was sooo much better. It started up smooth and warm up was smooth as well expect for a few small little blips on the way down to idle. I'm thinking those will disappear as the engine adapts to the newly clean intake valves. Engine feels smooth and so much more responsive while driving around. Alpina D mode actually isn't that bad anymore. Since your at 40k+ miles I recommend you get the walnut blasting done cause I was at 47k and mine were filthy

[I6+TT=FTW]

My SA explained it to me this way. On start up, especially cold start up, the engine is going through a warm up cycle, that is why the rpms jump to over 1000, then work its way down to 750-600 (depending on where yours normally sits). When you feel the little shakes and shutters during this cycle, it is because the injectors are firing up to 5 times per stroke, instead of just once.

Just my $.02

[fazman]

Originally Posted by I6+TT=FTW

My SA explained it to me this way. On start up, especially cold start up, the engine is going through a warm up cycle, that is why the rpms jump to over 1000, then work its way down to 750-600 (depending on where yours normally sits). When you feel the little shakes and shutters during this cycle, it is because the injectors are firing up to 5 times per stroke, instead of just once.

Just my $.02

Tell your SA that it shouldn't shake because it's no difference if you used your right foot to hold the gas pedal at any RPM value in Park/Neutral, your car should not shake (Otherwise new cars would have this behavior too).

He is trying to say your DME (and all computer controlled cars even back in the late 80's) would be in a closed loop O2 when it first fires up. Then after a few minutes it will switch to an Open loop O2. Your SA is telling you something true and correlating it with something unrelated.

Tell your SA, "Because the sky is blue, that is why he didn't win Lotto that week "