Hi All

I bought 03 S type 3.0 ...3 days ago. The car is clean..however i have a couple of questions but for now my major concern is that the RPM goes up and down by itself between 40-55 speed ( sometimes starts from 30)..then onces i go over 55, the car gets stable.

Please help me ..thank you

 

This is known problem called the "Lurch" and is a peculiarity of the 6 speed auto box introduced in 2003 do bit of research, it happens during warm up on light throttle or gradients.
Owners claim to have cured by adding Lubegard shudder fix or Platinum additive.
It doesn't appear to be terminal and at worst can be cured by a new Torque converter:
I would add the Lubegard Dr Tranny shudder fix first.

 

I don't think it's any lurch.

Instead, it sounds like the hunting problem (aka surging) often posted about (read the threads) and described in a TSB (free to download). Probably S307-14

 

If this goes away when the car warms up fully, then it is probably the software version as described by Jag V8.

 

Yes I stand corrected I said "Lurch" and brain was describing the other issue, an ageing brain is a hellish thing at times,
software update doesn't always cure it I used Lubegard.
The lurch if I remember was the Thunk as you come to a stop?

 

Thats all for helping answers. In fact it doesn't go away after warming up. However when it is happening, there is a sound coming up like am driving on the side-way alert bumps on high way [those little continues sequential bumps] !

 

Well in that case you need to get it plugged into a diagnostics machine, it could be drivetrain and not transmission or both but without codes it wont be easy.

 

Does the surging go away if you keep it manually in 4th gear at highway speed?

 

In fact, once I am over 50 it goes away completely

 

I'd start with a fluid change then.

 

I recall a recent thread describing a similar symptom...turned out to be a bad ignition coil. Search tool should reveal it soon enough.