Toyota is famous for building some of the most reliable vehicles on the market, but even the best cars are NOT perfect. No matter how bulletproof a Toyota engine is, it still relies on basic maintenance components to run smoothly. When a simple part like a spark plug starts to fail, it can cause severe driving issues that make your vehicle feel completely broken. 1. Engine Misfires and Rough IdlingA bad spark plug cannot produce the consistent spark needed to ignite the fuel inside the cylinder. When this happens, your engine will misfire. If you notice your car shaking or vibrating while stopped at a red light, your spark plugs are likely covered in carbon deposits or completely worn out. 2. Poor Fuel Economy (Wasting Gas)The truth hurts, especially at the gas pump. When spark plugs fail to burn fuel efficiently, your engine has to work harder and consume significantly more gasoline. If you notice your car is suddenly drinking more fuel than usual, replacing your spark plugs is the easiest and cheapest way to restore your MPG (Miles Per Gallon). 3. Hard Starts in the MorningAre you struggling to turn on your car in the morning? Worn-out spark plugs have a harder time creating the initial spark needed to crank the engine. This puts extra stress on your car starter and battery, leading to premature wear on your entire electrical system.Conclusion: Do Not Ignore the Warning SignsEven a Toyota will leave you stranded on the side of the highway if you neglect basic maintenance. Spark plugs are inexpensive and easy to replace, but ignoring these 4 warning signs can lead to permanent catalytic converter damage and massive repair bills.