1994 n/a Volvo 854

I just don't understand what is going on.

Beginning winter I was having a no start problem. So I went through steps and ended up replacing/cleaning parts until I got it started. Then I started getting this problem where the car just doesn't really want to go at low RPM's. The problem was such that I could still get around semi-reliably and even drove for an overnighter some 200 miles away. That was about a month ago. Since then the problem has worsened to an extreme. I have been replacing parts all along, trying to figure this mess out, but nothing seems to work. Some things make the problem disappear for a day and then, like a virus, it comes back even stronger than before. Just the other day it got so bad I had to park it, and after one trip to the bank yesterday, I just want to fill the bitch with dynamite. It wont go anywhere. I had the transmission replaced about a year ago and I had the same sort of problem just after. It goes like this now: as I give pressure to the accelerator, nomatter how much, the car simply shudders. The RPM's rise as intermittently as the car shudders, so there's no miscommunication there. Once I hit about 10 MPH the shudder releases a little bit - less often, longer duration per no-power. By this point I'm usually flooring it, and it will kick in and power through the rest of the gear most of the time. For months now I've smelled something like burnt sulfur or "rotten eggs" when I get out after driving any more than 5 minutes, and sometimes even while I'm driving. When I replaced the throttle switch last week, I erased all the codes, and there were none but the 1-2-2 when I checked today... which, when I'm driving more than 45 mph and pop the hood and put the car on auto pilot while I climb out and check to see if the 1-2-2 has gone away, is very helpful. So I'm happy for that.

The replacement list goes like this:

Fuel Filter
Fuel Pump Relay
Spark Plugs
Distributor Cap/Rotor
Spark Plug Wires
CMP Sensor
RPM Sensor
Fuel Pressure Regulator
Throttle Switch

I just filled the tank when the REALLY drastic shudders started happening and added some "fuel injector cleaner" just prior - at almost empty as per the instructions. I also ordered some stuff that claims to clean the gunk inside the Cat, but it hasn't yet arrived.

Please, can somebody please help me. I thought i was at the end of my wire before, but now....