It depends on what type of vehicle you own, mileage and year of vehicle. Usually its 10 years or 100k miles, whichever comes first. Easiest way to know is contact your dealer, notify them of your current mileage and ask if a tune up is due. REMEMBER; if applicable also replace your spark plug wires and distributor cap w/ rotor when doing a tune up!!! if you only change your plug you are simply changing the spark, not the current nor the distributing power.
Sparkplugs should be changed at regular intervals, it will usually state how often in the service manual and most garages will do it during a service regardless. It is no harm and often a good idea to check the sparkplugs yourself as the condition of the sparkplus can hint at other problems in an engine. See the following website for more details http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp Depending on the engine it can be a relatively straightforward task or an agonizing ordeal.
when there isn't enough spark going to the sparkplugs, and your car is not starting. sometimes it occurs most in winter because of the temp.
What does your owner's manual say? I would change them if the engine is not performing as it should, you are getting poor mileage, or you have over 75,000 miles on these plugs.
if the car is running rough or if plugs are in poor condition
Sparkplugs are almost universal, because of the way sparkplugs work and the way they are shaped the same, it means you should be able to use "standard" sparkplugs.
Sparkplugs do not truly enhance the preformance of the machine, as they simply arc and provide energy to burn the gas. Normal sparkplugs will do you with no change in milage.
You must buy BOSCH sparkplugs for this vehicle.
How often should you change the fuel filter?
about 3 hours
You should be able to reach around without unbolting motor mounts.
change sparkplugs on 2003 Rendezvous
I checked mine at 45,000 miles, and they looked brand new! Then I checked the owner's manual (should have done that first), and it shows a service interval of 100,000 miles.