I first noticed that when I went to pull away from a stop the car revved slightly before the transmission kicked in. this got worse and worse until when I pulled away it felt like the car had been rammed up the backside. I changed the transmission fluid and filter which cured the problem. The filter was quite clogged up so I guess the car had to rev a little to get the oil moving through the transmission to engage the drive.

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E61 525i 2004 M54 Auto
E46 320i 2002 M54 Auto
E46 330i 2003 M54 Sedan Manual