I have traced my cold start problem to the idle air control valve which appears not to be getting the proper voltage control signal from the FI ECU.
Unplugging the connector to the idle control valve results in no change to idle. If I apply 12v and ground to the valve (electrical connector off), it clicks open and idle increases. Based on this, I think the valve is ok.
There is 12v on the left prong of the electrical connector with the ignition on. The right prong of the connector is a very weak ground.
It appears to me that idle air control valve operation is controlled by ground resistance at the FI ECU. I am guessing that the ECU varies ground for the idle valve depending on reports from other sensors in order to increase or decrease idle.
The coolant temperature sensor appears to be operating within range. The over voltage protection relay is new looking and the fuse is intact.
I am not sure what to do now. Should I replace the computer and see if that solves the problem? Is there another sensor besides the coolant temperature sensor which could be causing a problem with the control operation of the idle valve?
To recap my symptoms, the car was not starting well at all when cold. Even when warm, idle seemed not quite right. On occasion, the car would start well cold, which led me to conclude the problem is an intermittent electrical fault.
Thanks,
Robert