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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > RPM instability on start - E90 LCI



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      03-10-2014, 07:35 PM   #1
chmsalman
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RPM instability on start - E90 LCI

Hey guys,

I've been noticing something strange happening with my car lately. It starts just fine but for the next 5-10 seconds or so, the RPM reading wiggles a bit between 500-700 (rough guess) before stabilizing. Once stable everything seems normal. Not sure if this is something I should be worried about, no warranty left on the car.

Ideas?
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      04-01-2014, 10:08 AM   #2
petelazro
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mine does the same thing for over a year now. it does it more when its cold. mine starts at 800 and jumps to 1100 and back and forth(i am in canada) then it slowly loweres itself to 600rpm.

From my research it could be a leaky injector or spark plugs. Once the car is warm it does not fluctuate even at a stop. My throttle response is okay but not that great. People with the same problem have changed their plugs and the problem has gone away. I have 122K KM on the car and i dont think i am waiting till 160K-KM (100K miles) hopefully it works.
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      04-01-2014, 10:11 AM   #3
Riick
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Spark plugs, time to change em
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      04-01-2014, 03:33 PM   #4
kaede
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Quote:
Originally Posted by Riick View Post
Spark plugs, time to change em
+1 if you haven't done that. Also, it might be dirty valves and or injectors, a quick easy fix is pour in a bottle of Techron Concentrate Plus - Fuel System Cleaner next time your fuel up - if its available in your area. Alternatively if you cant not find it at retail stores, they are actually readily available at BMW dealerships. They repackage the same thing to BMW branded injector cleaner or something like that. Good Luck!
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      04-01-2014, 08:42 PM   #5
chmsalman
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Nice, I'll try that! Hasn't happened recently so I might hold off on getting the spark plugs replaced.
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      04-02-2014, 03:41 AM   #6
chmsalman
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I have about 88k km on mine, when do spark plugs normally need to be changed?
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      04-02-2014, 01:20 PM   #7
kaede
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Quote:
Originally Posted by chmsalman View Post
I have about 88k km on mine, when do spark plugs normally need to be changed?
75k km on 335i, i think 328 is a bit delayed. Doens't hurt to change them though, preventative maintanence is the way to go especially for euro cars lol
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      04-05-2014, 12:20 AM   #8
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Half the normal interval if the car is tuned.
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      04-05-2014, 02:53 AM   #9
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the same thing is happening to my car, a little rough idle and fluctuation when start up but when driving and at a stop, its at a solid 640 rpm. I already changed the spark plugs but still the same, going to do valve cleaning and try the chevron techron injector cleaning next week.
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      04-08-2014, 04:10 AM   #10
chmsalman
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Quote:
Originally Posted by prepster View Post
the same thing is happening to my car, a little rough idle and fluctuation when start up but when driving and at a stop, its at a solid 640 rpm. I already changed the spark plugs but still the same, going to do valve cleaning and try the chevron techron injector cleaning next week.
Please report back with results regarding the cleaner. If it helps I think I'll definitely give that a try.
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      04-08-2014, 09:45 AM   #11
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I noticed my car doing that when the dealer flashed to the latest software for my n55. On cold starts, the engine hesitates a little bit for 2-3 secs and then comes alive.
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