1990 760 Turbo, 140K+ miles

1) We periodically have a problem starting the Volvo after it's been running for a while and has been turned off for only 30 minutes or so. We turn the key, depress the gas pedal and it tries to start but won't "catch." Finally, after 15 minutes (sometimes more) it starts up. Twice we wore down the battery and I had to use my Jeep to jump it. Once the cables were on, it started right up. This happens about once every week, but it is very frustrating, because we get stuck in places with no help! We've taken it 2 places - 1 place changed the ignition coil, but that wasn't it. The other place (they work on a lot of Volvos) changed the relay (I think that's what it was) but it still happens. We thought it was some sort of vapor lock but were told that because it was a Turbo, you couldn't have a vapor lock! ANY IDEAS??

The next problem may be related, so I'm including it here.
2) When it's damp out or we drive through puddles, it will sometimes just completely cut-off and come to a stop. We then can't get it started. We were driving about 40mph down a busy street and it happened. We were stuck in the middle lane with a "dead" car and had to push the car off the road. ANY IDEAS??

Note - if you couldn't guess, we're not mechanics so please try not to be too technical!! Even if you can tell us things that our mechanic should try, that would be great! THANKS