should be plugs only
 

Unless you need new wires, a tune up for your car should be plugs only.

Your model, fortunately, does not have caps and rotors (I'm pretty sure). If it did - you'd really be in need of a tune-up by now.

You can do plug wires if you want, but unless the resistance is out of spec, it may not improve anything.

Best of Luck,

Troy
1995 E420 83k

Do-it-yourselfer plug wire check...
 

The easiest plug wire check...

Raise the engine hood/bonnet on a very dark night...

With the engine warm and ideling observe spark plug wires area... [with total darkness no sparking should be seen]

If any "arcing and sparking" [tiny blue flashes of light] are observed, plug wires are faulty...

Another test was to have a spray bottle with fine mist adjustment, and spray misty water above the plug wires area and watch for sparking...

Only recommended if you live in a dry low humidity area...

The final test was to test internal resistence with an ohm meter on each and every wire...

The going rate is that each wire should have @1,000 ohms resistence...