1993 W124 Rough Idle...Bad Performance...
 

My 1993 300E has began to rough idle and has bad performance. Just started a couple of days ago., thought it might be bad gas. At highway speeds (60) can feel ever so slight hesitations. Is this the oxygen sensor? Bad fuel? Car is regularly maintained and it has 173,XXX mile on it.

check plugs to make sure they are in good condition, check wires and inside wire boots to make sure they are properly seated on plugs and distributor cap, then also check the O2 sensor. When was the last tune up?

Check the fault codes on the 16 pin connector in the engine compartment, which will require that you build the flash code reader. Try a search.

If it's a 1993, then it should have an M104. If it does, then it won't have distributor cap or distributor. Rather, it is probably one of the three coil packs. As Dean said, connecting a tester to the 16-pin test connector and doing a blink-code test will tell you which one. If the O2 sensor is bad, likely it would trip a check-engine light.

If it is a coil pack, it's a 30-minute job to change out. Best prices are on Bosch units at auto haus az dot com.

It was in fact bad plugs/wires. Car runs like new again. Thanks to all for the feedback!