mrtonyn

Now that the car has reached 100k miles and still running perfectly. Should I start replacing these original parts as a preventative maintenance?
1/idler pulley
2/belt tensioner
3/serpentine belt
4/crankshaft position sensor
5/complete spark plugs wire set

Note: dealership told me they do not sell the spark plug wire set ready to plug and play..would have to buy the parts and assemble the parts myself to make the spark plug wire. Then he told me they are lifetime and no need to replace them if I am not having issues with the wires.

Thanks!

Plutoe

If I were to take your approach, I would replace all the wires and belts that show cracks or small pieces missing and would overlook the mechanical turning parts until I started to notice unusual sounds.

01BlackE320

One of the very few parts that ever failed on my E320 was the idler pulley. It seized and caused my belt to snap and left me stranded. I replaced it and the tensioner. That was at about 110k miles. They're not expensive parts. The wires don't really need replacing on these cars. I assume you did the plugs though. I personally wouldn't change a crankshaft position sensor as maintenance. I have 155k now

mrtonyn

Good info., I plan on buying a kit from Amazon that includes the idler pulley, tensioner and belt for $160 and do it all in one shot.