I have a tip. and I have noticed a slight surge taking place between 2.5-3.5 rpm.This is a new situation. I am driving at a fairly constant speed, no heavy acceleration. Under heavy acceleration car runs fine. Was doing this before major service and still does it. Any clues? Thanks.

 

if you are 2002+ thats your Variocam Kicking in...

 

+1 on Variocam.

 

I had the same in a 99 tip. Cleaned the maf which helped but didn,t completly fix it.