cant recall the code but it reads cam position sensor malfunction but there is no such sensor on an 03 Ion , research shows that function is controlled by the electronic control module which i replaced and check engine light came right back on with the same code. . the engine still stumbles, anybody have any sugestions?

 

Does it misfire, like three cylinders? The coil packs fail and sometimes sets the cam sensor code. The module uses coil firing load to determine when number one fires. Then the car can begin sequencing the injectors. I have had a couple packs fail to fire #4 plug. The coil packs are really two double ended coils each firing two plugs at a time. 1 and 4 fire together and 2 and 3 fire together. The number 4 has the longest path past 2 and 3 and is the one that seems to fail first. You are correct that there is no actual sensor, it is inferred by the module.

 

I'm assuming the OP meant ignition control module, not ECM (for those who come across this later)...