The cold start enhancements are in the "E" part of the CIS-E system, which is why they are difficult to cold start if the OVP misbehaves.

My experience with older cars with electronics is that connectors can be a problem that cause intermittent misbehavior. It just takes a little corrosion on these low voltage connectors to cause problems, which are usuallly intermittent.

My suggestion is to remove the big multi-pin connector from the ECU, give the pins and receptacles a good inspection with a magnifying glass. Dress off any corrosion with a sharp metal tool like an Xacto knife or dental scrapper. DO NOT USE ANY KIND OF SANDPAPER!

Once everything is clean give the connector a shot of WD-40 and reinstall it. No guarantee, but it's worked for me in the past. You should also inspect the other connectors associated with the ECU - like the various sensors on the engine that are part of the system.

About 15 years ago I had an infrequent intermittent engine stumble on my Cosworth Vega that has what is essentially a Bosch D-Jetronic EFI system with those miniature Bosch connectors. I systematically did the above process with all the connectors on the ECU, injectors, and sensors. I didn't find any obvious problems, but the hour I spent on the task was worthwhile. The problem has not reoccurred since.

Duke