2001 Ford Taurus Check engine light

on my 2001 taurus the check engine light is on!!! the code reads misfire on cylinder 2 and 5 we have replaced plugs which were real bad, the plug wires, coil pack, pcv valve, and found no vaccum leaks. the problem only occurs at an idle the rpms drop to about 600 and idles real rough. when you start it goes up to about 1800rpms after about a minute it goes to 600rpms. after about 400 dollars parts and labor im tired of these mechanics who say ok its fixed.