My car back fire's sometimes when moving off and when I stop at the stop light. The rpms go down I put cleaner in the tank I changed plugs I changed oil I changed ECG nothing works can someone help me with this problem

 

You might want to recheck the spark plugs and the ignition coils and make sure they don't have oil in it. The last thing you need to check is the vacuum hose on top of the ignition coil on the passenger side. It is a small hose that has one end connected and the other end doesn't connect to anything. I used to have multiple miss fires with CEL on and the RPM dropping and reviving rapidly. Hope that help.