How can I get my Tecumseh engine to get more power and speed?

Why my 99 Camry v6 142k,miles the engine speed get faster in the slown down when i am aplly the same amount?

• why my 99 Camry v6 142k,miles the engine speed get faster in the slown down when i am aplly the same amount of pressure to the gas pedal at highway speed ? also on street driving like stop in go traffic when you press on the gas lightly soft u can feel the engine i dont know how to explain is like doesnt run smooth when you going soft u need to press on the gas pedal a little hard . I already change the spark plug. timing belt water pump, fuel filter, fuel injector cleaner , throttle body cleaner, new tps sensor, Any Suggest on this problem?

• Answer:

  Like it's hunting for a stable idle point.... Slowly up-&-down ?? Look for a vacuum leak.