If you get it into your own driveway - or if the shop doesn't mind if you work on it in their lot during off-hours - we can suggest a handful of likely culprits to check. Maybe you can drive it out of there! Things you could do with some careful pointers even without significant mechanical expertise - though you would have to be OK with getting your hands or knees dirty, etc.

I definitely wouldn't keep it at that shop for that mechanic to work on it! He's just replacing parts, hoping he'll get lucky.

I don't want to try to tell the non-Volvo mechanic how to do his job. A good way to get fouled up. If you don't want to get into it yourself - with help from this board - I think you'll need a mechanic who knows and likes rear-wheel drive Volvos.

Weak spark sounds suspicious. Maybe someone else will recognize it as indicating something. The coils rarely go bad, but ignition failures of various types will cause no spark.

My own experience stops at 1989/90 240s, so I'll leave the specific tips to others who know the 92s.
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Sven: '89 245, IPD sways, electric rad. fan conversion, 28+ mpg - auto tranny. 850 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).