what is the difference between a 305 electronic spark control module compared to a 350 electronic spark control module? it there a way to tell the difference between the 2 i think i might be using one on my 350 i swapped in. because the pervious owner blew the orignal 350 and just threw a 305 in it and i believe he put a 305 escm the car idles rough it has no vaccum leaks.

 

There isn't an external difference, one is designed to work with a 305 knock sensor and the other is designed to work with a 350 knock sensor. About the only way to tell by looking at it is if it has a label with the part number on it, the 350 escm is P/N 16128261.