1984 Chrysler Laser - stall when unloading engine

Hello,
I just recently acquired a nice 1984 Chrysler Laser (base model) with a 2.2L Turbo I. It's in good shape with a fair amount of restoration work done by the previous owner. I've been driving it around for about a week to work all the bugs out and I've managed to fix all the simple little things so far, but there's one problem I could use some help identifying.

When the engine has been running a short time it will want to stall when rolling up to a stop if you put in the clutch quickly and the RPM are >= 2,000. If you brake while leaving it in gear (5-speed manual) until the RPM fall to about 1,200 and then put in the clutch the idle will level off normally. When it does stall the engine does not feel like it is missing, nor does it "thrash" or feel like it is idling hard at all. The RPM just very smoothly sag away to about 600 and then if it drops further it dies. Sometimes it will "surge" a little bit to about 800 but then drop again. Other times it will dip low and then rise back to about 950 and stick there like a rock. If it just won't idle properly, holding the gas in just a hair (like up to just 1,000 RPM) will keep it running smooth with no variation in RPM.

If it does stall, it starts right back up with no problem and, although it still won't want to idle, if you don't bounce the RPM around too much you can get it to idle normally again.

Stop and go driving makes it worse especially if it was run for a while, shut off, and then started again. If you have been driving on the freeway for a while and then pull up to a stop you can put in the clutch at any RPM without worrying because at that point it won't miss a step.

No smells, no sounds, no unusual pressures (although the oil seems to stay a tad on the low side sometimes, but I think the gauge is wrong / sticking) or temps.

It might not be too big an issue right now, but it does act like the sort of thing that would get worse. I was wondering if anyone who was more familiar with these engines might have an idea about a common failure that would cause this. Various suggestions from my father (mechanic for about 30 - 40 years) include O2 sensor, EGR valve, and the fuel pressure regulator.

Thanks

EDIT: The cup on the end of the shift cable just broke... rats. Guess that takes priority over the funny idle (which, on the plus side, hasn't been stalling out).

Is your speedo working?

Yeah, the Speedo works correctly.

It blipped down to about 600 again today, but bounced back without stalling. Engine had just been restarted after a short trip, which aggravates it. I was testing my temporary "fix" on the shift cable (zip tie) so I was just tooling around.

Maybe I should correct that. The speedo "works" but I'm not so sure about "correctly" anymore. I paid a little extra attention to it today, and I noticed that when I'm dropping speed, right around the time that it is starting to idle funny, the speedo starts dancing back and forth. At other times it is usually pretty steady. It did go tweaky on me once on the freeway, though. It danced between 65 - 70 for a little bit when my foot was steady, but it straightened out. Starting to wonder if that wasn't a symptom of a funny speed sensor.

I'm not sure if it will still stall or not anymore, though. I figured the previous owner, with all the work he put into it, would have checked the PCV valve and lines. Today I had some free time, so I popped the tubes and the valve, and I found that the valve was worn out (loose; wouldn't seal), and the port into the engine was almost completely plugged with carbon deposits. The filter under the air filter was trashed, too. I cleaned out the engine port, the tubes, and put in a new valve and filter. After that, it started idling high around 1,600 - 1,800 RPM when I would come up to a stop. It settled down a bit, but still comes up to about 1,200.