The symptoms of a dirty throttle body include rough idle, poor gas mileage, faulty CEL codes, stalling and poor acceleration. Poor gas mileage is the result of the vehicle's ECU, or computer, attempting to adjust the fuel mixture to compensate for throttle plates that are incapable of closing properly. Faulty CEL codes cause various sensor-related issues, such as an illuminated check engine light.
A vehicle with a dirty throttle body experiences difficulty accelerating smoothly. Slowed and uneven acceleration is an indicator of a dirty throttle body. This automotive issue results in a hard gas pedal that requires more pressure to push down.
If the engine idles erratically or sputters when speeding up and slowing down, then the throttle body may require cleaning. Checking gas mileage is a way to diagnose a dirty throttle body. If a vehicle starts getting fewer miles to the gallon, then the throttle body requires cleaning.
The throttle body is a component of the air intake system, and a dirty throttle body can lead to air pollution. This issue leaves excess combustion products within the exhaust, which coats the inside of the throttle body. As a result, a dirty throttle body leads to poor performance and engine stalling.