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

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...