My 740 GL is very hard to start when the outside air temperature is at or below freezing.
When it does start, it runs very rough for a couple minutes and then is fine. This never occurs during
warmer weather. Has anyone else experienced this or have an idea what the cause is?

 

Check coolant temperature sensor that feeds the fuel injection. Not the one for the gage. Check for vacuum leaks. Check for bad orings around the injectors. You might also check to make sure the heater circuit is working on the o2 sensor. Just measure ohms but make sure you have the two wires for the heater circuit (they are usually the same color) You can damage 02 sensor if you inject voltage to the sensing side ususally green where it connects on the firewall. Heater just brings o2 sensor in faster to closed loop running.

 

I'm getting that now on my 940, and I suspect it is dirty or leaking injectors. The theory is that the nozzles are spitting gas blobs instead of creating a fine mist, so the fuel is having trouble burning until the combustion chambers become hot.

In addition to the good advice given by the 'Jeepster, you might consider having your injectors cleaned and flowed. Search for someone that provides this service (ask at a speed shop) or if you can afford the downtime, you can send them to an out of state service for as little as $12 per injector.

I'm searching local junkyards for extra injectors (I have REX-Regina injection) so I'll be able to send some out for repair and still drive the car. (The local FI guys want more than double the price per injector to clean).

Here's one site with some backround on FI Cleaning. (I haven't used these guys, there are others.)

http://www.accurateis.com/