2005 Dodge Neon Computer Codes

I am having trouble with my engine not wanting to idle correctly. The service engine light has come on and off and I have had it tested twice. The first time they told me it was the spark plugs, ignition coil, or the fuel pressure was to high or low. My husband replaced the plugs and the coil, but the light has come back on and is doing the same thing. Now they tell me that it is still the fuel pressure. I am wondering if you could tell me if that is quite possibly the gas cap or maybe just the fuel filter and line? If it is how hard is it to change the fuel filter in this car? I thank you for any help.