The service guide and warranty book for my '08 250 indicates that at 72 months or 60K owner should replace spark plugs with a footnote that says, "Required under the terms of the emission control warranty." My car just hit 6 years but only has 41K miles. Should I change the plus anyway? I figure they are not warn out but don't want to mess up the emissions warranty or have Lexus say I did not maintain the car as required and fight me if I need the 9 year extended warranty for major engine work due to the carbon build up and poor idle. I had the top engine cleaning done when the car started idling poorly at 20K before Lexus started offering the major repair and am not optimistic the issue won't come up again. Thanks!

 

Yeah, I'd do it just so when the carbon build-up problem comes up again the dealership cannot blame you. It's a good preventative maintenance thing anyways.

 

change them according to book.

 

I would go by mileage and not years

 

I am the type of person who is uncomfortable with major parts like this sitting for too long so I would just change it for peace of mind.

If you want, you should look at some major spark plug brands because they have different change interval than what is recommended by Lexus. For instance, Lexus says change oil every 5k miles yet Mobile 1 Oil website says oil change interval are good for up to as long as 15k miles. NGK doesn't have a specified spark plug change interval but brands like autolite, champion and AC Delco have change intervals that says 5 years OR 100k miles, which ever comes first.