E34 540i/6 Running rough

[Evil-E]

You check the casting number on the block near the passenger side block drain plug for the coolant yet? Before you spend a ton of time and money trying to "fix" your issue, make sure you aren't dealing with a nikasil block. You'll have to research the block casting numbers but you want an alusil block, not nikasil. Just my .02 cents.

[JoeMadoo]

yo id try putting premium in your car cause i let my old man drive my car for a while and he put regular in for a while got that same noise then i put premium back in the noise went away fast!

Yeah I use good gas. I think if you heard the sound in person it would change your perspective.

You check the casting number on the block near the passenger side block drain plug for the coolant yet? Before you spend a ton of time and money trying to "fix" your issue, make sure you aren't dealing with a nikasil block. You'll have to research the block casting numbers but you want an alusil block, not nikasil. Just my .02 cents.

I have the alusil block. But from what I've heard, if you have a nikasil block and it's made it past the 90's, you will be fine.

[Aleksey]

Assuming nobody touched your timing from my experience I will bet it's a vacuume leak.

The easy way to test it is to grab vacuum gauge and read pressure of your manifold if it fluctuates or below the spec you got a leak.

You can also spray brake cleaner if you don't mind mess and interaction of chemical with your plastic parts.

Spray around manifold AND around fuel injector o-rings on top and bottom part of injectors those are prone to failure before seals fail on bottom of the manifold. Don't forget obvious spots such as front and back of manifold that PCV and trottle body plug in (including small TB sensor mounted on the side of the plate).

The 02 sensor code can be thrown if you have vacuum leak, our DME is too basic to recognize improper reading as anything but a faulty device.

If you did everything else but could not find the culprit AND get 02 bank code, swap the 02 sensor (just plugs no need to take them out) and reset the code. If same bank is throwing error it's a mixture and NOT the sensor.

I would also check your fuel delivery rate under load to make sure it's not choking. Blocked fuel filters are rare for this car but weak worn out fuel pump is not.

[Jean]

Check the basics first obviously, such as vacuum leaks, bad plugs and/or boots, get a DMM and check each coil. Check Fuel pressure as well when running....