I didn't actually post this problem to the forum, but I read a lot of other posts on the subject. The 1.9 has a problem with very low idle, car has to be run for a couple of minutes on the first start of the day just to get to run well enough to keep from cutting off, and even when it stays running the rpm's sit at about 500 at idle.

I saw a lot of approaches - IAC, MAF, vacuum, throttle body, various sensors - I was throwing parts at it and getting nowhere. I tried all of them as well, and no change.

By accident, I noticed a small set screw behind the cable pulley on the throttle body. It isn't immediately obvious that it's adjustable, as the allen key end of the screw is covered with blue paint, apparently put in at the factory (I saw the same in two other S40's in my local junkyard).

Once I realized it was adjustable, it was just a matter of getting the right allen key and adjusting it until the car was idling properly.

When my car first started acting up, the change came on fairly quickly, just a week or two from running decent to barely starting at all, so a factory set idle stop screw wasn't the first thing I thought of, but I've been running over two weeks now with the adjustment and it's purring like a kitten.

Here's a link to the screw location
https://www.brickboard.com/IMAGELIB/volvopic.htm?js_link=1&id=13131