I have a 1995 USA W124 with a 104 motor.
It was running poorly and I changed the MAF meter and it runs great now; until I get to 3100 RPM, the car balks at 3100 and just shutters unless I take my foot off the pedal, then it up shifts, the RPM's fall and all is well.

If I'm going at highway speeds I can dwn shift manually to 3rd (the car is an automatic) and the revs are >3100 the motor is smooth but if I apply the gas again it balks.

Any ideas?

Thanx

 

Your car may have a restricted catalytic converter due to carbon build-up from earlier running problems. A quick test would be to remove the upstream o2 sensor and drive it. I know it will be quite loud, but if it then runs right up past 3,100 rpm you will have confirmed the restriction is there.