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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > Help! RPM fluctuates!!



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      12-28-2005, 05:33 PM   #1
E90330iSMG
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Exclamation Help! RPM fluctuates!!

hey guys!! my 330i auto currently has 4800 miles. and somehow the RPM needle is VERY unstable! it moves up and down about 100 rpm when its idle with a/c off sometimes, and with a/c on ALL of the time. when i'm accelerating, i feel like the rpm is shakey too!! also when i set my car on cruise control, the rpm needle has the same effect as the idle movement, it moves up and down abruptly around 100 rpms up and down!! i'm sure this is coming from the engine instead of just a unstable tachometer. please help me and tell me what problem it is or if you have had the same situation!! Thank you guys so much for the help!!
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      12-28-2005, 06:59 PM   #2
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Quote:
Originally Posted by E90330iSMG
hey guys!! my 330i auto currently has 4800 miles. and somehow the RPM needle is VERY unstable! it moves up and down about 100 rpm when its idle with a/c off sometimes, and with a/c on ALL of the time. when i'm accelerating, i feel like the rpm is shakey too!! also when i set my car on cruise control, the rpm needle has the same effect as the idle movement, it moves up and down abruptly around 100 rpms up and down!! i'm sure this is coming from the engine instead of just a unstable tachometer. please help me and tell me what problem it is or if you have had the same situation!! Thank you guys so much for the help!!
ok well my friend has a civic and it has an intake with a trap on it so it will not pull too much air into it i took it out to mess with him and his rpm started to do the same thing it would just go by it self up and down from 1 to 2k and just stop this happens when the car is getting too much air and starts to rev it self to not turn off i would say go down to bmw and show them if it does not happen then tell them to look at your intake they should see somthing wrong there....
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      12-28-2005, 07:23 PM   #3
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A qualified BMW dealer can answer this and fix it (but you knew that )

Could be idle control valve, could be a VANOS issue too, or a intake/exhaust cam timing problem, or a vacuum issue. Are using 91+ octane feul (without mixing any grades) ?
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      12-28-2005, 07:26 PM   #4
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Originally Posted by JackMac
A qualified BMW dealer can answer this and fix it (but you knew that )

Could be idle control valve, could be a VANOS issue too, or a intake/exhaust cam timing problem. It could also just be normal, 100RPM isn't way out of spec. You using 91+ octane feul?
fuel does not make a difernece its the intake too much air
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      12-28-2005, 08:39 PM   #5
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I'd get it checked - that is abnormal... or abby someone.
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      12-28-2005, 08:46 PM   #6
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thx for the responses guys! ya i'm running on 91 for every mile of this car, but from different gas stations. this makes me wonder if i should still install the K&N air filter...
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      12-28-2005, 10:55 PM   #7
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Quote:
Originally Posted by E90330iSMG
this makes me wonder if i should still install the K&N air filter...
Have the problem fixed before you quite possibly compound the situation with a double problem.

I an VERY weary of changing the air filter. Not sure if it such a good idea. Make sure you check to see if the cover needs a gasket or sealent once the filter is replaced.

All the best in your endeavours.
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      12-28-2005, 11:01 PM   #8
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Hey, mine does the same at idle. It fluctuates about 100rpm as well.
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      12-28-2005, 11:23 PM   #9
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This hasn't happened to me or I haven't noticed anything like this yet. I would recommend that you take it to your dealer to get checked out..

Good luck
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      12-29-2005, 02:08 AM   #10
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Maybe a software update will fix this

The dealers computer will tell them if there is anything wrong when they hook it up
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      12-29-2005, 03:08 AM   #11
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no offense to anyone here...but if that happens to you wouldnt you just take it to the dealer??? I mean sure you can get opinions here but in the end you still have to take it there.
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      12-29-2005, 04:53 AM   #12
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Quote:
Originally Posted by BMWE90
no offense to anyone here...but if that happens to you wouldnt you just take it to the dealer??? I mean sure you can get opinions here but in the end you still have to take it there.

But then the forum wouldnt enlighten anyone about anything and it would be just people talking about how much they love/hate their E90.



I've notice my rpm vary a bit, and thought it was somewhat abnormal. It did phases of a 10 seconds high, then a few low, around the 600 to 800, dont remember exactly where.
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      01-03-2006, 04:27 PM   #13
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stretch

Sounds like a coil getting ready to expire.
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      01-04-2006, 01:02 PM   #14
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Quote:
Originally Posted by stretch
Sounds like a coil getting ready to expire.
Doubtful. Most likely a sensor mis-cal or malfunction.
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      01-05-2006, 06:34 AM   #15
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The last thing that I would recommend is to replace the stock air filter element with an oil wetted element prior to complaining about idle fluctuations! The second to last thing I would do is replace the factory type treated/pleated paper air filter element with an oil wetted element on a street vehicle, ever!
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      01-05-2006, 07:32 AM   #16
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i do know whenever the engine is started, it will start a bit above 1k rpm and slowly moves back down and a little bit of swing. i am sure it is nothing abnormal.
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      01-05-2006, 08:50 AM   #17
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Quote:
Originally Posted by coreslogic
i do know whenever the engine is started, it will start a bit above 1k rpm and slowly moves back down and a little bit of swing. i am sure it is nothing abnormal.
This is typical of most engines nowadays. Its a coolant temperature activated idle valve adjustment. As the coolant heats up, the idle valve is closed further and further until you reach your average ~700 RPM.
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      01-06-2006, 12:34 AM   #18
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Got the same problem with my 320i. The fluctuation is always there, cold start or warm engine, with or without A/C. However I did not notice any changes to engine performance. Brought it back to the agent and they could not determine what cause the problem. Only thing they said was this problem exist on some E60 engines and suggested that I ignore it and leave it alone since it does not affect performance. Almost told him to go to hell, but that was right after Christmas. What if the engine died on me after the warranty period? After much complaints, the manager promised to investigate and get back to me in the New Year (hope its 2006). New Year resolution - kick some asses in BMW till they resolves the wind noise, squeaky wipers and the fluctuating RPM.
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      01-06-2006, 07:29 AM   #19
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Quote:
Originally Posted by E90330iSMG
hey guys!! my 330i auto currently has 4800 miles. and somehow the RPM needle is VERY unstable! it moves up and down about 100 rpm when its idle with a/c off sometimes, and with a/c on ALL of the time. when i'm accelerating, i feel like the rpm is shakey too!! also when i set my car on cruise control, the rpm needle has the same effect as the idle movement, it moves up and down abruptly around 100 rpms up and down!! i'm sure this is coming from the engine instead of just a unstable tachometer. please help me and tell me what problem it is or if you have had the same situation!! Thank you guys so much for the help!!
Have you had this checked yet by the dealer so we'll know what it was? I believe CIP20 also mentioned addressing fluctuating idle.
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      06-24-2006, 01:15 AM   #20
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Quote:
Originally Posted by JackMac
Have you had this checked yet by the dealer so we'll know what it was? I believe CIP20 also mentioned addressing fluctuating idle.
Same thing here. I got 2300 miles on the car now and think I might pay the dealer a visit. Wonder if the fluctuation is normal for it to go up and down around 800-700RPM at idle. BTW, I have been using BP 93 octane gas since I got the car on May 27 06! The car is less than a month old.

Regards,
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      06-24-2006, 01:19 AM   #21
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noticed the same thing on mine a while back. Took it to the dealer and they said nothing's wrong with it...
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      06-24-2006, 04:42 AM   #22
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after about 3 months i noticed my car was running a little rough, and on cold starts, the rpm would fluctuate

during my service, the dealer updated my software (for which they kept the car overnight - does it take that long !?) now it runs very smoooth again and seems to be more torquey in the 1000-2500 rpm range

havent revved it right up since the service, but will once i get the change =)
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