Oldsmobile/Buick Repair: Idle Jumping, o2 sensors, vacuum line

Question
I own a '98 Olds Intrigue with the 3.8L with a 150K on it.  I've noticed recently while driving the car seems to buck badly around 35mph.  I noticed that the tachometer jumps up and down approx 200 rpm.  I've had a similar problem at 100k miles and it turned out to be a misfire caused by bad wires but I just changed to new Gm wires and the problem still exists.  No engine light has come on.  Is there anything else to check.  I still have the original O2 sensors.

Answer
Could be numerous possibilities uch as a residue builup on the throttle plate area that needs to be cleaned off, A possible cracked vacuum line somewhere on the engine, The o2 sensors need to be tested using a scanner, Could be a faulty fuel pump pressure regulator and or the start of a fuel pump falure.

All these items need to be tested.