no throttle

ok......if a throttle response is the ability of the engine to respond to your input from the gas pedal, what causes this? It is a symptom of some greater problem or problems right? What is a possible direction a mechanic may be guided? Or in otherwords, can you give me a long answer like you gave with the "no crank" question. That one was extremely helpful and it was not vague in understanding. It answered well enough for a judge to make a good decision on that basis.... =)