99 eclipse idle drops and sometimes stalls at complete stop
 

I have a 99 eclipse 2.0 non turbo rs. Ever since I got the car it had a misfire and a terrible idle to it. I have done everything I know to do.. I changed the plugs and wires, the IAC, the fuel filter, cleaned the fuek Injectors . I got a check engine light the other night heading to work due to a misfire finally shown the code of the crankshaft sensor. I replaced the sensor and have no more misfiring problems.. everything seems to be checking out okay. the only problem I cant seem to diagnose is when I come to a complete stop at a stop sign my car idle drops to about 100 rpm then after a couple seconds it comes back up and runs very efficiently. what could my problem be???? ANY SUGGESTIONS????HELPPPPPPPP