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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Rough idle at cold start...



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      11-03-2010, 09:19 AM   #1
EastCoast335i
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Rough idle at cold start...

So recently as the temps have been dropping close to freezing I've been experiencing rough idle on cold start-up...
After the car warms up a bit the idle is fine...
This is my first winter with a piggyback tune (sstt was on previously) and I never experienced this in the past 2 winters.

I'm wondering if the tune has something to do with it???
I also unplugged the exhaust flapper connector for the first time this winter, so maybe the rough idle is due to that???

Trying to diagnose the problem one piece at a time, just plugged the exhaust flapper back in... I'm going to see if that fixes the rough idle...
If not I'll scan for codes and remove the tune...

If anyone has experienced this, any feedback would be appreciated...
Thanks
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      11-03-2010, 10:55 AM   #2
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I'm also experiencing the same thing. The rough idle is most likely your car misfiring due to bad fuel injectors. It's quit common for this to happen regardless if the car has a tune or not. If your car is under warranty pull the mods off and take it to the dealership.
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      11-03-2010, 01:07 PM   #3
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Bad fuel injector
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      11-03-2010, 01:24 PM   #4
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Quote:
Originally Posted by e90_guy View Post
Bad fuel injector
If that were the case why does it only happen on cold starts and only for a few minutes?

Wouldnt a bad fuel injector cause issues warm or cold?
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      11-03-2010, 02:12 PM   #5
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My car does that with no tune. Very common for these cars to run like sh1t when cold. With the tune, it still happens so its obviously not the tune.
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      11-03-2010, 02:38 PM   #6
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As far as I can tell it happens to everybody, I am going into the shop tomorrow to see if the injectors/spark plugs/coils need to be replaced. I can garuntee that its one of the 3. Do some searching on old threads because this is a very common problem. I will post on here tomorrow about what they said about mine.
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      11-03-2010, 03:24 PM   #7
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Its the injector leaking overnight and sturating the spark plug. When you first start the SP is wet with fuel causing your misfire. They replaced my fuel pump first with program update. Then the next day after it was still misfiring they replaced all 6 injectors plugs and low pressure fuel sensor. HTH
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      11-03-2010, 03:28 PM   #8
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Quote:
Originally Posted by EastCoast335i View Post
If that were the case why does it only happen on cold starts and only for a few minutes?

Wouldnt a bad fuel injector cause issues warm or cold?
You've fuel slowly leaked into the cylinder and that's why it only happens in cold start. Your car returns to normal after the excessive fuel is burned.
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      11-03-2010, 03:30 PM   #9
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Quote:
Originally Posted by 02themax View Post
Its the injector leaking overnight and sturating the spark plug. When you first start the SP is wet with fuel causing your misfire. They replaced my fuel pump first with program update. Then the next day after it was still misfiring they replaced all 6 injectors plugs and low pressure fuel sensor. HTH
Thats what I figured, now the goal is to get it replaced under warranty with all these mods lol
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      11-03-2010, 03:33 PM   #10
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Quote:
Originally Posted by e90_guy View Post
You've fuel slowly leaked into the cylinder and that's why it only happens in cold start. Your car returns to normal after the excessive fuel is burned.
So if you go by that...that means we can rev it up to 2kish for about 5 secs and that should burn the excessive overnight fueling. If that dont work i call bs?

btw my car did this after 200 miles it now has 26k and still doing it.
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      11-03-2010, 03:36 PM   #11
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Quote:
Originally Posted by Tee212 View Post
So if you go by that...that means we can rev it up to 2kish for about 5 secs and that should burn the excessive overnight fueling. If that dont work i call bs?

btw my car did this after 200 miles it now has 26k and still doing it.
No spark = no burn...
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      11-03-2010, 03:40 PM   #12
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Quote:
Originally Posted by Tee212 View Post
So if you go by that...that means we can rev it up to 2kish for about 5 secs and that should burn the excessive overnight fueling. If that dont work i call bs?

btw my car did this after 200 miles it now has 26k and still doing it.
Nope, I agree with him (02themax). I have read lots of threads on this and he is correct. How would revving it up for 5 seconds help the leak during start up? The corrective measure would be to fix the leaking injector...there is no other solution. As soon as you push the start button it will begin to studder, so how are you gonna fix the problem after it already occured lol??
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      11-03-2010, 03:40 PM   #13
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Quote:
Originally Posted by 02themax View Post
No spark = no burn...
compression + a/f + spark = burn ....got it
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      11-03-2010, 03:45 PM   #14
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Quote:
Originally Posted by Penn999 View Post
Nope, I agree with him (02themax). I have read lots of threads on this and he is correct. How would revving it up for 5 seconds help the leak during start up? The corrective measure would be to fix the leaking injector...there is no other solution. As soon as you push the start button it will begin to studder, so how are you gonna fix the problem after it already occured lol??
Thats what im saying, since he figured the injector is leaking...how long should it take to burn it ALL off? 1-10 mins idle time? wouldnt reving it up speed up the process? So we all have leaking injectors soon as the car leaves the show room floor?
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      11-03-2010, 03:52 PM   #15
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Quote:
Originally Posted by Tee212 View Post
Thats what im saying, since he figured the injector is leaking...how long should it take to burn it ALL off? 1-10 mins idle time? wouldnt reving it up speed up the process? So we all have leaking injectors soon as the car leaves the show room floor?
It burns off immediately but before you press that start button there is an excess of fuel in the cylinder (which bogs down the engine) and then is quickly burned off. You should not sit and let it warm up which I just learned the other day, Im not sure who posted on this? Maybe clap135? but its actually in your bmw manual. It says to start her up and drive right away. Im not gonna get into the tech side to it but if you do some searching on here you will find out why you shouldnt...as far as us all having leaking injectors...No, its kinda like the hpfp. They degrade over time, especially those of us who have highly modded engines and added stess is put on these engine components.
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      11-03-2010, 03:57 PM   #16
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I know about the idle thing man lol, rings are cold so theres no expansion so youll just contaminate the oil cause premature wear to the cylinder walls blabla. It was just just for troubleshooting sakes to shot down the leaking injector theory. Theres been ppl with bad hpfp under 1k. Like ive said earlier...ive experienced morning miss fires with 200 miles on a brand new car.
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      11-03-2010, 04:40 PM   #17
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I wouldn't worry about it - my car idles rough (noticeably shudders every few secs) when cold, but sorts itself out when warm (as oil temp pases 1/4 mark).

Remap has made cold startup slightly rougher, but Ii don't mind because once it's warm it flys!

One tip my mechanic gave me - every month, take a cruise in low gear with revs between 4-5k rpm to get the cylinder temp up (engine can take it). You'll notice oil temp pass 1/2 mark, then I usually back off. Aim is to burn off carbon deposits in the cyclinder so allow your engine to run more smoothly. See if that makes a difference...
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      11-03-2010, 05:05 PM   #18
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Quote:
Originally Posted by jagdeepj123 View Post
I wouldn't worry about it - my car idles rough (noticeably shudders every few secs) when cold, but sorts itself out when warm (as oil temp pases 1/4 mark).

Remap has made cold startup slightly rougher, but Ii don't mind because once it's warm it flys!

One tip my mechanic gave me - every month, take a cruise in low gear with revs between 4-5k rpm to get the cylinder temp up (engine can take it). You'll notice oil temp pass 1/2 mark, then I usually back off. Aim is to burn off carbon deposits in the cyclinder so allow your engine to run more smoothly. See if that makes a difference...
I will be interested to try this out...
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      11-03-2010, 06:10 PM   #19
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Quote:
Originally Posted by e90_guy View Post
You've fuel slowly leaked into the cylinder and that's why it only happens in cold start. Your car returns to normal after the excessive fuel is burned.
Ok that makes complete sense... BUT how come it only happens on cold starts?

If the injector were leaking fuel regardless of outside temp, shouldnt i be seeing rough idles every morning whether its warm or cold?

Are you saying the injector only leaks when its cold out?
I'm no mechanic/engineer by any means, but I'm just trying to understand the logic here.
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      11-03-2010, 06:48 PM   #20
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Quote:
Originally Posted by EastCoast335i View Post
Ok that makes complete sense... BUT how come it only happens on cold starts?

If the injector were leaking fuel regardless of outside temp, shouldnt i be seeing rough idles every morning whether its warm or cold?

Are you saying the injector only leaks when its cold out?
I'm no mechanic/engineer by any means, but I'm just trying to understand the logic here.
No, its not just on a cold start. I believe when he is saying a "cold" start he is meaning when the engine is completely cold. As in....has been able to sit for several hours and totally cool off. It is just more evident in the colder weather.
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      11-03-2010, 10:35 PM   #21
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Quote:
Originally Posted by Tee212 View Post
compression + a/f + spark = burn ....got it
What would the point of revving your engine be if your spark plug is not sparking due to already excess fuel??

OP you might be able to smell the extra fuel on start up and possibly have a slight (very slight) puff of smoke.
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      11-03-2010, 10:44 PM   #22
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lol thats why one would rev to burn off the excessive fuel, dry plug + no excessive fuel means no miss fire right? but whatevers man you know best.
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