You know I have been having the same problem and have not been able to figure it out, but thanks to you I may be able to fix it now. The only questions I have are how much did you pay for the ECU, and was it hard to replace? I have an 82 245 and I cant get the idle to work right when the temp is above 30 degrees, but if it in the 20's it high idles and runs rough but it does run. But I still have a rough idle that I think may be the throttle body being dirty. I really want to get this fixed so if you have more info about what happened to your car it would be great. My Aux air valve works fine and has been cleaned.

Here's a list of what I and a volvo shop have done,

New coolant temp sensor-Me
New injectors-Me
New injector o-rings inner and outer-Me
Idle set-The shop
Fuel air mixture set-The shop
New o2 sensor-Me
Multiple tune ups-Me
New exhuast manifold gaskets-Me
New flame trap-The shop

I love this car but I hate the crap it puts me through, and that shop charged me 200 dollars to tell me that the o2 sensor was bad and the flame trap had popped off. Plus another 175 bucks to set the mixture, the idle and to replace the flame trap, so as you can tell I am pretty much on my own with this car and I am at my wits end. Any help you or anyone else can throw at me would just be awsome, thanks everyone.