Whats the definition or "rough idle" 540i\6sp

[wmann]

I see the term rough idle and vacuum leaks hand in hand here and was wonder what defines a rough idle.

I have a 1995 540i/6sp that I had a compression and leak down test done on prior to purchase and all was fine. I didn't drive the car over the winter and just started driving it this spring.

Love the car, lots of power, a blast to drive, But I do notice some vibration at idle.

The idle holds at about 500 rfm on the tach, no surge or variation. The vibration is not a real shaking but its noticeable.

The indy that I used to check a leak that was discovered in the spring (power steering fluid) said the drivers side engine mount should be replaced. Reading the posts it seems that this is a common side effect of this type of leak, but is not noticeable until 2k.

I get about 17 mile MPG mostly city, and was normal and how much vibration is transmitted in other people cars....

Thanks for any help that you can provide!

Bill Mann

[632 Regal]

the V8s do not idle silky smooth because the cams are a bit on the radical side. Does it clean up right off idle?

[Blitzkrieg Bob]

transmitte the vibration into the frame and make it more noticable.

[wmann]

Its not noticeable when moving, I will see if I give it some gas at a stop has the same vibration, but I would guess not.......



the V8s do not idle silky smooth because the cams are a bit on the radical side. Does it clean up right off idle?

[632 Regal]

these have a harmonic vibration at about 2200 rpms too (duey knows what rpms the V8s do it at)

[digitaldragon03]

Its not noticeable when moving, I will see if I give it some gas at a stop has the same vibration, but I would guess not.......
Usually it still rocks when giving it gas at a stop, but not as dramatic as if it were idling at a stop.

[Tiger]

Sounds just like my car... normal. Our V8 have hot cam so it is not super smooth at idle... a tad lumpy is the way to describe it.

[winfred]

i read one place talking about the failing nic motors with the door all of the way open the end of the door moving a 1/2 inch up and down with the idle

[digitaldragon03]

Why did we get special cams?

[632 Regal]

i read one place talking about the failing nic motors with the door all of the way open the end of the door moving a 1/2 inch up and down with the idle
when my Nikasil was failing the door did move a lot. plug boots repaired it.

[Tiger]

Did you noticed how fast our RPM accelerate? That's why... BMW designed these engine as semi-racing engine... which is why our torque is at higher RPM... Then they decided not to do this on the 4.4L where their gobs of torque is available at much lower RPM.

[Tiger]

Yep, if you had a failing Nik.. the door would shake tremendously up and down when opened... Otherwise, normal enigine would shake just a tad.

[wmann]

Not concerned about engine failure, unless the BMW dealership totally botched up the leakdown and compression test. The door movement is not visable with the door open at idle, but if I put my hand on the door I can feel some movement as I would expect.

I was more interested for the fuel consumpsion aspect, I don't expect the world, but if I could get 20 mpg instead of the 17 I get now I would be very pleased.

What does everyone esle get for MPG??

Thanks for all the input! Bill Mann

[632 Regal]

my 530 tops out at 22 mpg.

[digitaldragon03]

Did you noticed how fast our RPM accelerate? That's why... BMW designed these engine as semi-racing engine... which is why our torque is at higher RPM... Then they decided not to do this on the 4.4L where their gobs of torque is available at much lower RPM.
The car does seem to accelerate better at higher engine speeds. I wonder why BMW decided to do this.

Anyways, now im worried, my door does shake noticably when its open and i havent warmed up the car. I would say it does move up and down around half an inch. The only reason I havent thought much of it is because it only happens in mornings. Once its warmed up, the idle is pretty smooth. I always thought that the nikasil rough idle would continue even if the car had already been warmed up.

[winfred]

that sounds like a intake gasket leak, ether one of the port gaskets or the throttle body, it usually kicks up some 02 sensor/lambda codes after a while. while i have the intake off i do all of the gaskets and the pcv plate


The only reason I havent thought much of it is because it only happens in mornings. Once its warmed up, the idle is pretty smooth. I always thought that the nikasil rough idle would continue even if the car had already been warmed up.

[SharkmanBMW]

if it only runs rough when it is cold it could be the rear part of the intake manifold, pcv plate.
I think that is the name, mine was rough at start up and would smooth out after a few minutes, I changed that part and it went away - sweet!