Cel light an low idle cold
 

My version 3 idle runs low when cold once it's warmed up it's fine, I've changed the lamba, water temp sensor, plugs, my car has an apexi ecu an the cel light comes on at idle, goes off when driving and comes back on when off throttle, I unplugged my apexi and plugged the original ecu in and the car won't start and the cel light just continuously flashes every second, when I plug the apexi back in it's like one cylinder isn't firing then clears itself and runs fine. Am struggling with this one, anyone help or point me to what's going on
Ps this problem was going on before I changed the parts

Read the error code and rule out guessing . . .

There is no error code it just constantly flashes, no pauses no fast or slow flashes, when the black connectors are connected