Does it stop at 3500 rpm, is it a proper hard judder/miss or more of a stutter and loss of power for 500rpm?
In order of cost only:
Search U281 buy one and scan it (could show up a bunch of faults, I bet you have a wheel sensor gone

)
Search relays and change them.
Search crank position/angle sensor, change it
Search throttle body position/reset, Free but needs vagcom