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I had my spark plugs and wires changed some 80,000 miles ago. I used expensive NGK iridium spark plugs. It is supposed to last over 100,000 miles. Recently I experienced deteriorating gas mileage: only 26-27 miles. There are several factors for that. I cleaned the fuel injector and checked everything else and I found nothing was wrong. I had tried to pull out spark plugs in the past, but I couldn't because the spark plug wire boots were stuck. I finally bought new wires just in case old ones are torn during removal process. I used a channel lock pliers to firmly grip the base of the boot and managed to lift off the boots. When I removed the spark plugs, the gap was wide open and the condition of electrodes were not good. I bought new Champion platinum plugs. They were much cheaper: around one-third of NGK. After changing the plugs and wires, I calculated gas mileage again. Wow! The result was surprising: Now gas mileage jumped to 33.8 miles per gallon! It was great improvement. The odometer hit 275,000 miles today. Now I can drive 400 miles with one fill-up. I don't think I need to buy a new car. My conclusion is that you don't need to spend a lot of money for iridium spark plugs, but buy economical, but dependable Champion platinum spark plugs and check regularly and replace if necessary. Iridium plugs are supposed to last long, but there is a risk if you keep too long in the engine and that they can be stuck and difficult to remove and moreover, they don't really last long.