[MATTY Lz]

I notice after putting my 2009 335i in park it gives a very slight rev every 1 minute or so without touching the acceleration peddle. Its very faint but I can feel it in my feet as if its a car beside me revving. Has anyone here experienced this also?

[Jeff@TopGearSolutions]

Sounds like a small boost leak / Vac Leak.

What other modifications are done to the vehicle? How many miles on the car?

My gut feeling is its one of the vacuum lines although if the mileage is a bit higher you may just be due for spark plugs or an intake valve cleaning.

[MATTY Lz]

The car currently has 43,500 miles on it.

There are no modifications on the car and here is a list of service work done:

@ 16k km - HPFP replaced.

@ 41k km - Replaced vehicle battery.

@ 43k km - Replaced 3 fuel injectors/3 decoupling elements/3 High Power spark plugs.

@ 57k km - Replaced 3 fuel injectors/3 decoupling elements.

@ 60k km - Replaced left exhaust silencer & exhaust flap.
@ 60k km - Replaced coolant hose coupling

@ 65k km - Replaced B+ Battery Cable.

@ 69k km - Primary Catalytic converter/Pressure Converter/Exhaust pipe with Catalytic Converter.

That brings us to the end of the previous owners lease.

[akotten]

Are you just feeling this? Or does the tachometer register the change too?

[MATTY Lz]

I just feel it as well as here a very faint rev. The tachometer does not register the rev though.

[007_e350]

if its very slight it could be just needing walnut blasting or one of the spark plugs going out ... but before changing anything put a bottle or two of chevron injector cleaner

[MATTY Lz]

Ok, Ill give that a try then. As long as its just a spark plug and nothing too serious.

[Sigma 3]

That's not going to stop it. My car does the same thing. It sounds as if a fan clutch or alternator clutch is spinning freely. I've rplaced plugs and cleaned valves a year ago. Still making that reving sound

[ashmostro]

Don't be offended by this question, but is your radiator fan turning on in concert with this increase in revs? Any accessories on, like ac?

[MATTY Lz]

Originally Posted by ashmostro

Don't be offended by this question, but is your radiator fan turning on in concert with this increase in revs? Any accessories on, like ac?

lol I would never take offence to any questions, I'm the noob here. But no its not, all accessories are off as well. If the A/C was on I wouldn't be able to hear the rev but perhaps still feel it in my feet. (1 minute intervals like clock work). I'm knew to the car also so it could just be a normal thing that my 2002 Volvo S80 didn't do hahah.

[MATTY Lz]

Originally Posted by Sigma 3

That's not going to stop it. My car does the same thing. It sounds as if a fan clutch or alternator clutch is spinning freely. I've rplaced plugs and cleaned valves a year ago. Still making that reving sound

So it hasn't led to anything bad Ill take it?

[Sigma 3]

No sir. Not yet. I will keep you posted in this thread if I come up with something

[Jeff@TopGearSolutions]

If it's any consolation this car was never known for the smoothest idle. Now that I read more into your potential problem it almost sounds normal. Although it still could be an indication of a minor boost leak, spark plugs, intake valve cleaning, or even leaky fuel injector. The latter is usually attributed with a very bad idle and rough start though.

[007_e350]

try one more thing, take out the vanos and clean them with carburettor cleaner and plug them back it - my idle used to go up to 750 on idle at times, but it stayed there, was v frustrating ... vanos cleaning solved that, there's a DIY here if u search

[MATTY Lz]

Ok, Ill try a Vanos cleaning and see if that does the trick. Other then that Ill keep an eye on the above mentioned issues.

[Sigma 3]

Originally Posted by Jeff@TopGearSolutions

If it's any consolation this car was never known for the smoothest idle. Now that I read more into your potential problem it almost sounds normal. Although it still could be an indication of a minor boost leak, spark plugs, intake valve cleaning, or even leaky fuel injector. The latter is usually attributed with a very bad idle and rough start though.

Jeff, I don't think it's the engine at all. When this first started happening to me I would be sitting at a light and think somebody next to me was reving as if to race me.the sound is pretty pronounced but it's all so clear that its separate from the engine. maybe a turbine wheel perhaps?