1995 C280 has a couple issues that could cause poor running/mis-firing. One is the degradation of the main wiring harness in the engine bay. The other is a faulty Over-Voltage Protection (OVP) relay.
Have both these checked.
Also, the above post is correct. Check electrical ignition components...
For your vibration? Tires, wheel balance, steering components, suspension components, driveshaft parts, etc. Big list of things...
1998 C230 "Black Betty"