I have a 2001 Ford Mustang that has started hesitating when i'm accelerating. when I rev the engine while it's in neutral it doesn't seem to have the problem. I already replaced the spark plugs to no avail (But they REALLY needed to be changed) before I go out and spend hundreds on spark plug wires/ coil pack/ fuel injectors i was wondering if you had any ideas. I watch your videos from time to time and I really enjoy them. Thanks in advance

tune it up first with spar plugs and air filter and go from there if needed

I replaced the air filter and spark plugs but it's still running rough. I also used some fuel system cleaner.