So I pulled my engine redone my timing and put a new head on my liby and I was having start issues I figured out that I had to replace my air idle control sensor, I replaced that it started fine with a rough idle but ran. It then gave me a throttle position sensor code I replaced that now it won't start at all. I checked my wires to make sure the connection was good, and still nothing so I put the original one back on and still no start.it back fires and won't start. Anyone know where to start?