what year was the s2 made? that is deffo a early s2 inlet manifold, the s1 inlet manifold is 2 peice and that one is clearly not, there are 2 possibilites i can think of as to why u have a non knock sensor inlet manifold and ecu but have a knock sensor connector

1. the original engine has been replaced with a earlier one and the early inlet has been left on and the earlier ecu has been used too

2. the loom has been changed


now if the car is a late 87 early 88 model then more than likely its had a engine and ecu swap

if its a 86/ early 87 car then its likely to of had a new loom for some reason

personally id just buy a knock sensor inlet for £20 fit it with ur new red blue black chipped ecu and hey presto all is good