Planning to have my spark plugs changed for a 2005 Toyota Sienna. Should I replace the coils as well every time I change the spark plugs at 120,000 miles?
No.
No, no need to do the coils. This is the procedure I followed when doing my 2008 Highlander a couple of years ago.
https://www.youtube.com/watch?v=ING-RK7NJ-c&t=613s
There should be no reason to replace the coils. I just got back from my local Toyota dealership today getting some maintenance done. I hate the stupid oil filter on the 2007 so I have them do it at $70 but my wife only drives about 4k miles a year so I only have it changed every year. I have a Sienna with 128k on it and they wanted to charge over $600 to replace the spark plugs. It's not an easy task to get to the back three plugs but you can do it yourself if you have the spare time and the tools. Toyota recommends replacing the sparkplugs at 120k.
