I have the very same problem with my '94, 940 Turbo wagon. In the morning she fires right up, but after sitting in the hot sun, she just turns over and fails to catch -next morning...starts first try. Any ideas? Thanks.
Okay; here's the deal. Evidentally there is an issue with the circuts on a Fuel Pump Relay (located above the fuse block in the center console). Because the cars have been around for a while, the circuit board inside Fuel Pump Relay expands when the car gets hot inside causing the circuit to open...hence no signal to the pump to send fuel to the engine. This is likely the cause. It's an easy to do, and you'll save yourself labor cost.
Note: The actual relay is the square block in the second row from the top (underneath the round one). The part is about $50 US. Hope this helps.