The screws are in elongated slots in the TPS body so the switch can be rotated back and forth for adjustment just by loosening the screws. You of course will have to re-adjust it properly once you've turned it, but if the switch isn't clicking there's really no other choice.

You're not going to hear the TPS click when the engine is running (leastwise not without a stethoscope). In quiet surroundings, with the engine not running simply turn the throttle spindle by hand to open the throttle. Just as it's opening you should hear a faint, but distinct click from the switch and it should click again as you return it back to the closed position just before it reaches the stop. If there's no click then you need to loosen and/or remove the TPS switch for more thorough checking. If you still can't get it to click then it's at that stage you use a meter to verify the switch is indeed faulty when there's no change in continuity between pins 1-2 as the switch is opened/closed.

BTW, as you have seemingly learned, when you're all done make sure the throttle cable is properly seated in the correct spindle groove otherwise the throttle can't reach the fully closed position.

Your mechanic's thought about replacing the MAF sensor (AMM to us Volvo types) is way, way too premature. If he's actually stuck his nose under the hood and knows what he's doing then I'm afraid calling him a Volvo mechanic is being a bit too generous. Yes, a failing AMM can cause stumbling, although hesitation is usually how it would better be described, but more often than not these Volvo AMM's fail outright and cause a no-start. One proper way to diagnose a bad or failing AMM when the engine won't start or is running particularly poorly is to disconnect the AMM (with the key off) and attempt a restart. This forces the ECU into what's called "limp home mode" where it ignores sensors like the AMM. If the engine now starts and runs better than before then it's the AMM, otherwise the AMM is just as likely okay and it may well be something else. An even better way to diagnose a faulty AMM is to borrow a known good working AMM and swap it in as it only takes a few minutes. There are only a couple of different AMMs used on the old B230 engines and any decent Volvo mechanic worth his salt will have known good spares on the shelf just for such occasions. As long as we're on the topic here, and as others may be following, using special MAF/AMM spray cleaner is more often than not a worthless and perhaps even fatal attempt at trying to restore funcionality in this type of AMM with a burn off heater cycle. I've learned that lesson more than once.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now