I agree, likely multiple problems going on. If you go through it methodically, exactly as you plan, you'll hopefully soon have it figured out and without having to throw too many unnecessary parts at it. It takes experience to find the fine lines between replacing a part for the heck of it, doing some initial diagnosis and testing to find out what doesn't need replacing, making sure adjustments are correct before replacing something, and doing full testing to confirm exactly which component is responsible. It's made all the worse when there are multiple problems going on. There are circumstances where each of those approaches is appropriate. After all these years keeping my Volvos going, using experience, a collection of reference materials and following various Volvo forums, it's a very rare day I unnecessarily replace an ok part. Having two nearly the same 940s, I do have the advantage of often being able to swap in a known good part to confirm a diagnosis.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now