I have read the other postings but have not been able to figure out what is wrong with my Mustang. I just bought a second 3.8 litre 2002 Mustang. The cats have been removed and it is backfiring and has a rough idle. It has a new coil pack, plugs, and wires. I have replaced the IAC and TPS and the air filter. When I bought the car the previous owner had put all of the plug wires on in reverse order. When I changed them to the correct firing order I gained power but there are still some issues. Looking for help so I can avoid throwing money at the wall to hope something works. I have a new fuel filter and will put it on tomorrow, but I was thinking since the plugs wires were put on wrong all of the plugs may be fouled out causing this problem. What are your thoughts??????

 

If it's running rough and backfiring, it sounds like you still may have 2 wires crossed.