I have a 2004 525 with 36,000 miles, lately when I am coasting down a hill or even flat roads the tach needle has been jumping up and down. In about 1000 tach range, back and forth. This is under no acceleration, just coasting. You can even feel the car accelerating and decelerating a little. When driving under normal acceleration every thing is fine. Has anyone else experiences this? What could be making this happen? Thanks for input!

 

From what I understand this sounds like classig gear hunting. That is if you have the auto tranny. This could happen if it doesn't know wether to speed up, slow down, wait or whatever. So it decides do to something, and you get the mild acceleration and slight RPM increase, and if without input from youm slow down again. This could happen if the auto tranny has not decided yet your way of driving and is constantly adjusting. I'm not sure, but I think this would be helped by a software upgrade, which I'm planning to get for my 2006525i. I've seen o the forum that the upgrade improves the dancing steps between the engine and the tranny. I you have the manual 6 spd... Beats me...

 

Thanks for the info DRG. I do have the automatic, sounds like that could be the problem. I am going to my dealer to check it out. I'll see if there is a software update available. Thanks again.

 

As to the software change, SI B 61 14 03 (March 2007) says that Progman 25 will correct a problem in which "the speedometer and tachometer needles shake when the vehicle is idlling." This may not be your issue, but it could be a reason to seek the Progman change.