It’s not uncommon for these motors to have a slight miss at idle, especially on the old f20's. Sometimes a bit of oil slipping past the rings or valve guides will weep a little oil into the combustion chamber causing a audible miss at idle. In this case it’s usually not apparent when driving, if it misses under acceleration then you have a problem that needs to be dealt with. If the plugs look ok and the car feels strong, no severe idle surging and no CEL codes come up ...then I’d forget about it. You may be getting nit picky.