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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > N53 325i low RPM fluctuation



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      08-11-2022, 03:52 AM   #1
KalevE
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N53 325i low RPM fluctuation

I have had this problem since I got the car last year. At first I didn't notice it but that was probably because it shows only on specific conditions.

Video of it: https://photos.app.goo.gl/YRLDVcE8wAVHHcSW7

In the video the car is standing still on P and I am pressing the accelerator just a little bit. My foot is at the same position the whole time.

As you can see, the RPM goes up and down in quite a large amplitude. If I rev it a bit more, let's say 2000 RPM, then the needle stays put. I guess therefor it is not noticeable while driving even when using cruise control (RPMs too high)

Last year I went to the dealership and also visited 2 different indies and all thought that it is caused by bad injectors which the car had too. Heard only one alternative thought that maybe a fuel tank over pressure valve (or something like that) is leaking.

Anyways the car now has new injectors (under 2000km on them), NGK spark plugs and Bosch coil packs (under 10k km). Recent jobs also include new thermostat, water pump, new pulleys and belt, oil and filter and oil cooler gasket replacement.

Problem still it is reproducible 100% of the time I try it no matter the outside temp, humidity etc.

Does anyone have thoughts about this?
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      08-11-2022, 08:33 AM   #2
Phil325i
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So what happens when your foot is off the gas? I wonder if your foot being partially on the pedal is confusing the throttle body into overcompensating...
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      08-11-2022, 02:20 PM   #3
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Seems to idle OK-ish I would say, especially when AC is engaged and with new injectors installed. Haven't noticed fluctuations while, let's say, waiting behind a red light etc. Error logs were clean too last time I checked.

But I wouldn't say that it 'purrs like a kitten'. IMO my previous diesel M47 was almost the same noise and vibration wise except the occasional lifter tick.

Before getting the N53 I thought the six pot petrol engines would be much quiter than diesels but what do you know...
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      08-11-2022, 04:19 PM   #4
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The n53 is a little like a diesel at idle but if you actually put it next to a diesel it is actually much quieter.
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      08-12-2022, 03:07 AM   #5
KalevE
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You are probably right I am just a bit OCD when it comes to car noises

On the road the engine sounds just fine and after swapping out the old and loose hood sound dampening pad with new STP stuff, it became quieter still.

The fluctuating RPM still bothers me a bit but maybe it is the throttle body adjusting too much.

Would it be worth replacing vanos solenoids? Don’t see them being replaced before and car has 170k km on the odo.
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      08-12-2022, 06:34 AM   #6
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Quote:
Originally Posted by KalevE View Post
Would it be worth replacing vanos solenoids? Donít see them being replaced before and car has 170k km on the odo.
At that mileage it can do no harm. And I would replace the Vanos filter/check valves too.

Piezo injectors are notoriously noisy. If you like it quiet, make sure your cosmetic plastic valve cover is always in place and that the sound deadening foam on the reverse of the cover is in good shape. Also, some models didn't have the under-hood sound layer fitted. Can easily be retrofitted if you want to...

Part numbers: check valves (x2) 11367541692
Under hood cover: 51487059260
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      08-14-2022, 12:49 PM   #7
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Regarding new vanos solenoids. I read from some thread that supposedly Uro and Pierburg are better (and cheaper) than OE. Are they worth getting? Any other brand that's recommended?
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      08-14-2022, 04:58 PM   #8
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Quote:
Originally Posted by KalevE View Post
Regarding new vanos solenoids. I read from some thread that supposedly Uro and Pierburg are better (and cheaper) than OE. Are they worth getting? Any other brand that's recommended?
As the solenoids are fairly vital components, I'd need some persuading to buy other than OEM. But that's just me...
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