Bubba-Ugly

I have 1990 5-speed, non-turbo Legacy with 315K miles on it. The engine will not stay running after a cold start unless I hold the throttle open a bit with my foot. After it gets hot, the engine will idle, but then the CEL illuminates and stays on for the remainder of the drive. It will not go off until the engine is stone cold again. Electric resistance on the ByPass Air Valve (a.k.a. IAC) is around 9.6 ohms. It is receiving a 12V signal. Any ideas?

I own a '90 Legacy AWD 5-speed with 310K miles on it. About six months ago the Check Engine light lit up on the dash. I read the codes (11, 13, 24, 31, etc) and tried to make sense of the. I disconnected the battery for an hour, and when I reconnected the light came on again with the same codes set. I went looking for the ECU, but have not found it. I wanted to check it with another ECU. Any ideas out there?