Idle problem.Thought fuel, but it was bad ECU
I would suspect a marginal distributor pickup situation or bad connection, IE
marginal reluctor gap
poor magnet, etc in the pickup
poor / corroded connections in the connectors
So far as 4/5 pin you cannot tell by "looking." You must check continuity of the 5th pin, as some 4 pin boxes (I have several) still have the 5th pin physically in place