Another possibility is your tb is gunked up on the manifold side and you just haven't seen it. Lots of tarry buildup in there can stop your butterfly valve from closing properly too, or more particularly blocking the little bypass passage which is your mian contibutor to air intake at idle since the butterfly is usually set almost or totally closed. It blocked = less air = slow idle. Adjusting your idle screw up is letting more air in but eventually you'll run out of adjustment. I took my tb and manifold off a few years ago because I was having idle problems but adjusting the idle screw was only fixing temprorarily. Problems would still come back. Finally took it off and it was very dirty. After a good cleaning I reset my idle and everything was a ok. The clean manifold and tb made a huge difference to performance and smooth running too. Mileage up a bit, and more power too.

Just a thought in case the problem reterns later after you adjust the idle screw.

F