Question on BMW 3-Series E36 O2_Sensor

[dr.e36]

Hi. I have a problem with my 320i M52 '95. The acceleration is uneven. During this, the fuel consumption gauge is swinging up and down by several liters. Any ideas for the cause?I need your help. I have a problem. My e36 320i M52B20 (oct.'95) (275000 kilometers) accelerates unevenly most of the time (about 95%) and during this the fuel consumption gauge sways - rocks up and down evenly about once every second or less for a few liters (metric unit - about two pints) in each direction.
(I am not from an English speaking country so I hope "fuel consumption gauge" is the correct phrase - the thing that shows fuel consumption under the RPM meter).

Of course, the gas pedal is kept perfectly still during this, so the problem isn't due to my leg shaking or anything like that

The previous owner of the car and I studied the problem quite extensively. The phenomenon is not due to any external factor, e.g. wind, road. It happens in all situations. It does not matter whether the car is cold or at the working temperature (although when I have been driving it for 1 hour or so, the acceleration is higher and the fuel consumption much lower, but that is probably normal and due to engine materials being evenly hot and properly dilated)

1. It happens when the gas pedal is depressed from about 1/4 to 3/4 of the way. At low acceleration and at full throttle the acceleration is even, however I think it is not high enough for this engine.
2. The biggest differences in acceleration are seen between 2000 and 4000 RPMs. Above that it is much less pronounced.

Follow this link to see the video, made by the previous owner of the car around 2 years ago:

During this experiment, he held his foot perfectly still on the accelerator. The rocking of the fuel consumption gauge can bee seen above 60 kilometers per hour (above 2000 RPMs, driving in the third gear):
http://tinypic.com/player.php?v=6oh28l&s=5


3. While driving at a steady speed and same gas pedal position (again on a straight road and not on a hill or anything), the car very finely but distinctively accelerates and decelerates, again the consumption gauge mirroring the effect.

This may be important, however it is a recent issue and was not present for almost two years since the problem was first seen: A couple of times when I started the car, one cylinder, I think, didn't work, so the problem could probably be a spark plug, spark plug cable or the top of the thing that divides the current among the spark plugs, right?

This also might be important: Sometimes when I press the pedal, the car doesn't immediately start, but waits and then slowly starts to accelerate.

I don't know if it is related or if it is normal for this engine, but below 3000 RPMs the acceleration is in my opinion very low. Above this barrier, the car is a rocket compared to below it.

I have to ask the previous owner, if he replaced something and after this he noticed the problem or if it couldn't have been related to anything.

- I replaced the rubber hose that connects the airflow meter with whatever is behind it.
- The car didn't show any problems when my mechanic hooked it up on his tester. The spark plugs looked normal and the cylinders didn't show any unusual deviation from normal data.
- The airflow meter was replaced by the previous owner.

My mechanic thinks that the problem could be that somewhere there is air going in through some crack. That would cause the vacuum to drop and would cause the problem in his opinion.

Any comments and ideas will be greatly appreciated! Thank you in advance!

Bye
Thank you!

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This post was auto-generated based upon a question asked on our tech article page here:

[Nick at Pelican Parts]

I would check your oxygen sensors. be sure they are not stuck or bias in one direction, rich or lean. This would be a good place to start.

- Nick