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Old 01-11-2013, 11:54 AM
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DFEL750I DFEL750I is offline
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Join Date: Apr 2010
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Mein Auto: 750I
Originally Posted by Piers1989 View Post
Thanks for the information.

As the box was just replaced, the fluid is new and has been filled to the correct level. Also there are no leaks.

The RPM seems to stay ABOUT level when idling, but if im honest it doesn't idle as smoothly as my old 745i did, you can feel it occasionally through the car.

I haven't really tired putting my foot down since I got the car back, but it seems to set off fine.

From doing more driving and being aware of an issue I've realised to power deliver when it does fluctuate does feel a bit unsmooth, and I was thinking that if rather then "bouncing around" on cruise, the revs are actually just dripping then rising then is it possible that the engine is causing the fluctuation and the torque converter is actually masking some of the issue by allowing some slip from normal operation?

I know in most auto cars as you adjust load when under very light load the rev needle doesn't stay directly synced with the speed. (My old volvo, proton, mates 335i)

Does that make sense or am I talking out of my ass xD
If the RPM is fluctuating when the engine is not under load in P or N then you have to fix that issue. When the engine is under load it would only be worst. The fluctuating idle can be cause by a number of factors that would screw up the air, spark, gas ratio within the engine. This includes....vacuum lead, bad mass air flow sensor, bad coil, bad spark plug, bad or leaking injector, bad O2 sensor etc. The only way to know is to have the car diagnosed.

If you have INPA you can check to see which cyclinder is not idling smoothly under the engine options. I dont remember under which menu exactly but there is one of the display functions that shows you each cylinder...INPA gives you a number...the further the number is from 0 the less efficient that cylinder is running. Normally you will just see one that seems and little different compared to the rest. If you can find that cylinder you can start by swapping the ignition coil in that cylinder with one that is idling smoothly to see if the problem follows the coil. If it doesnt follow the coil then do the same thing but this time with spark plugs. Past that you are looking at another issue but this is a good place to start
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