What would cause a rough idle and a lean condition (15.5-16.2 afr) at cold start only. Once it goes to closed loop everything is fine and if I restart it later, everything is fine in open loop. I have logged the cold starts with Datamaster and everything looks fine except the RPM (obviously) and timing drops to around 20-24 (no knock retard).

 

Check the coolant temp sensor reading at cold start. If its reading higher than actual temperature, the extra fuel added as part of the cold start enrichment will not be as great.

 

I checked it out and the temp starts at 76 and gradually climbs from there.