First order of business, thanks to everyone that was so helpful with diagnosing stalling problems for late 80's early 90's Volvos. This is my first post ever, and I made an account just to see if I could pay it forward and help someone else with this issue.

My car is a 1991 Volvo 740 non turbo wagon. My symptoms were : stalling only while idling, especially coming to a stop while the car was running. It would get to where I would randomly lose all engine power, only being able to go 1 mph with the gas pedal to the floor. Then after about a minute or 2, it would pick back up and work fine while driving at normal speed. It caused me so much anxiety because where I commute to is stop and go traffic for about 30 minutes of my 50 minute commute. I would stall at a stop light, restart my car, which did so without a problem, only to be met with the car losing all engine power. I had "idiot!" yelled out someone's window at me a couple of times because I literally could not move out of the way. I got to where I would hold down the brake pedal while revving the engine when I came to stop lights so that I didn't stall. Even then, it would try desperately to stall out on me.

This was about 8 months ago when the problem began. I first took it to my mechanic, who is actually the one that sold me the car, and he said the fuel filter was bad. So we changed that out. It worked like it should for about 2 weeks, then began again. I took it back to him because I thought it wasn't just the filter but the fuel pump. He changed that out as well. That time it worked for a few months and I thought all was well. Nope. It started again. I figured the chances that a fuel pump going bad was very low, so I began looking online for what else could be causing the issue. I cleaned out the throttle body, I cleaned the IAC valve, I replaced the fuel pump relay, I cleaned out the MAF. I check all the fuses just to be sure. I replaced the fuel pressure regulator. Nothing worked.
I took it back to the mechanic and he said it was the plug wires, that they were arcing, so he did a tune up. Helped for a day or 2 then the stalling resumed. I replaced the battery, which was about time for it anyways. That helped for a day, then back to the same problem.

I again took it back to the mechanic. He said it was a "gummy fuel line". It worked for a few days, then back to stalling. So I told him it was still happening and he said he just had surgery on his shoulders and that he'd call me when he was back. I didn't have time to wait because I could get stuck in the middle of an intersection and die from an accident.

So I began taking matters into my own hands. I was getting OBD code 233 which was the IAC valve signal missing. So I went back to cleaning the throttle body and IAC. They were still pretty clean from when I cleaned them before, but I recleaned them anyways. What I didn't notice last time, was the plug had corrosion on it, a greyish buildup. So I scraped that off and thought for sure that would solve the issue.

Also, I read in the forums to CHECK YOUR VACUUM LINES. so I inspected them and found where someone had very poorly spliced them together. There was a cut going down the length of the tube so I duct taped it, and was almost positive that would be the last of this problem. The next day, it did decent going to work. However, after work it lost engine power and stalled the worst it ever had. So I pulled over to double check I had put everything back the way it should be, and everything looked good. But when I went to take one of the hoses off that runs to the throttle body, the connector piece began to disintegrate my fingers. I had my duct tape on me a d figured I'd tape it up to see if that's what was causing the issue. I have not had a single problem since. No random sputtering, no loss of engine power, no stalling at all. I had found the issue.

So, long story short, check your vacuum lines very closely. And scrape that crud off of your IAC plug!

 

Here is the tube I taped up that seems to have fixed the problem. Just for reference. It is a rubber connector on the end of the tube that connects to the nipples on the throttle body.
Thanks to everyone that gave great advice as to how to fix this issue!!

 

looking at this picture of a 91 turbo I had (long gone), I'd guess that line goes to the carbon vapor canister purge thing, but I'd trace yours and see where it goes to be sure. it looks to be generic vacuum hose.