my car mileage went down and very slow on taking off. on 2007 Toyota Yaris

At how many miles do i change the plugs? My car has 40K.
Are the original plugs Iridium?
If so, can I use cheaper plugs?

Asked by for the 2007 Toyota Yaris
Iridium plugs will last 60000 miles easy. I have seen the air flow meter start to fail and cause poor performance and gas mileage to drop without setting a Check Engine Light. May be worth trying to clean it, it is delicate only use a chemical parts stores will have it CRC product # 05110 , it easy two philips screws hold it into the air filter hosing.
2 answers
Toyota recommends to replace the 4 Platinum/Iridium Spark Plugs at the 120,000 Mile Service. They may not be the cause of those problems. Use the RepairPal Directory to find an Auto Repair Shop or Mechanic; http://repairpal.com/directory?address=11419&car_brand_names=Toyota