Also check your fast idle thermo valve, if it's stuck open then it's bypassing too much air past the idle air control valve (IACV) and making the idle wierd. You would only notice it at low RPM because it's such a small amount of air compared to what it needs under any kind of load. Does the temp gauge read correctly??

I have no idea what to tell you about the fuel filter, try that first, you should do that anyway if you don't know the car's history.