it's a 1999 S70 T5 with automatic tranny, and at highway spped when trying to maintain speed, it will tend to buck a little, it feels like a fuel issue (like it's starving itself and then corrects itself)
it happens whether I use the cruise control, or try to maintain speed myself.

car only has about 63K miles on it and has been dealer maintained. Is under warantee until next january, and I'd like to actually get it diagnosed. Does anyone have an idea (vac leak? ETC system?) It has not set a code (yet)

hello
could you please explain a bit more re: "buck a little".....what happens with revs ?

Similar thing happened on my '00 S70 40Kmiles. After a while I got the ETS light. Dealer replaced both the sensor and trottle module. I was lucky the car was under warranty, otherwise its expensive as the earlier post has mentioned.

I'll just hope it fuly fails in the next 6 months, in the meantime, I'll complain about it every trip to the dealer (I figure if I bring it for oil changes and such they're more likely to go to bat for a prementioned problem) until it does go.

his is spookily like the issue that mine had before the Throttle Control packed in.... You may notice the same behaviour when it is under light loads in other gears too... mine did it in all gears and just when it was lightly loaded. If you can get it sorted under waranty then do so as it is $$$$$ to fix!

Good luck