Help Economy mode auto is rough, Power is smooth

I've just bought a 97 BMW 323i. (150ks / 65000 miles) Test drive etc was fine, driving it home, I noticed it was VERY rough at about 100kmh (60mph), I rang the previous owner who said it sometime happens in
economy mode (auto) and change to sport mode, this should fix it... and it did. Puzzled! Any ideas? I was going to do a transmition fluid change this week not sure this will help....
Any ideas my dear BMW afficondos?
Karl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 10 Oct 2007 04:03:14 -0700, snipped-for-privacy@gmail.com waffled on about something:

Did the roughness come or go when the torque converter by-pass engages? You can usually see/hear when this happens, get yourself to a nice cruising speed, say 60mph, and then feather the throttle a little, when the bypass engages the revs will drop about 500rpm, but with no loss of speed.
Does this have any effect on the noise?
Dodgy.
--
MUSHROOMS ARE THE OPIATE OF THE MOOSES

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Oct 10, 12:03 pm, snipped-for-privacy@gmail.com wrote:

What's the mileage on the car? Doesnt sound to me like it's a trans problem but rather something else. I'm assuming sport mode drops it down a gear?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

65000 miles.. No cruising at 65 mph it should be in top gear regardless of sport or economy mode... I dont believe it's a wheel balance or suspension issue, I'd experience it regardless of the mode the auto is in.. Perhaps a fault in the ECU mappings for economy mode where it doesnt provide enough fuel or similar mioght make the car shudder?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Most BMW setups disable the highest gear in sports mode - it's an economy cruising gear.
--
*Growing old is inevitable, growing up is optional

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 10 Oct 2007 16:30:17 -0700, snipped-for-privacy@gmail.com wrote:

Wrong David. Sport does not engage 5th gear in an auto
--

Sir Hugh of Bognor

The difference between men and boys is the price of their toys.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Oct 12, 5:29 am, snipped-for-privacy@h-gee.co.uk wrote:

Ok, you guys are right... 5th? must be disabked in sport mode and is responsible for the rough running. Thats bad news, must mean my gearbox is due for a major looking into!
5th kis a funny gear to go... I know of them going on high torque vehicles, ie Toyota Landcruiser diesels, but 5th in an auto wouldnt get much of a flogging I'd think. Now to find a local auto transmition specialist that doesnt charge me my firstborn to have a look....
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I don't know the country where your car was originally sold, but US spec cars may have a totally different make auto from Euro ones. Including being a 4 rather than 5 speed.
Again depending on country etc the torque convertor lock up clutch may only work in the highest gear - so it might be that giving the problems. If it were oscillating. So it *might* be a rare fault which can be cured without gearbox removal and a subsequent full overhaul. You'll need to find a good honest specialist. Good luck in that.
--
*Microsoft broke Volkswagen's record: They only made 21.4 million bugs.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You don't say what you mean by "rough".
If you run the car in the region of 90 - 100kmph you are near the point at which the box changes from 4th to 5th. The gearbox may hunt (change up and down a lot) in this case, especially on cruise.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.