Mackschmitt

I've recently been having problems with my 1997 Legacy Outback 2.5l I am the second owner, and have never had any real issues with this car. Swapped out alternator and starter, and cleaned and fixed a vacuum leak within the EGR system, all this over the course of 6 years of ownership (so, nothing huge or costly). I have 25,000 miles until my next timing belt change. In April I took it in to a mechanic because it was coding for the EGR system again. . . They couldn't find anything wrong with the EGR and said it was the knock sensor and replaced that. However, the check engine light kept coming back on and they couldn't figure it out despite my subsequent 3 visits to have it looked at and the code pulled (their assurance was that it was the knock sensor, and that it just needed to go through a drive cycle). I took it to a different mechanic (whom a friend with an 03 outback trusts), and he found 3 issues with the EGR and fixed it for fairly cheap. The check engine light has not come back on since. HOWEVER, since getting the knock sensor replaced in April my outback will randomly idle roughly, and has since gotten worse. More recently it will start up oddly (it kicks over, but it's almost like it's not getting gas but hitting the throttle doesn't change), it idles rough at stops, and when I hit the gas after it idles rough the RPMs drop suddenly before the car goes. . . It feels like it's going to stall out and die but never has. It has, however, died/stalled twice when it's idling rough and I put it into park, but always starts back up. The only thing that seems to make a difference--If it has sat overnight it will work perfectly the first time I drive it anywhere. If it is idling rough, if I "gun it" and speed up fast it will usually clear the symptoms and it will drive fine for the rest of the drive. And it seems to be worst whenever I am stopping frequently, i.e. stop to get coffee, stop at the grocery store, stop to get gas. . . With frequent stops the problem seems to get worse. Hoping for an easy fix (and without the blessing/guarantee from my mechanic it would work), I put a new throttle position sensor in it, but the problem persists. Has anyone had anything similar to this?