Mysterious Regina problem

[Thomas8]

Hello, I have a 1990 740 sedan non turbo with the Regina system in it. It ran rough when I bought it from an older lady that drove daily but not far. I was under the impression the car hadn't been properly warmed up in years hence the roughness. She said she had the fuel system replaced as well as the cap, rotor and ignition coil. When I got it I swapped the MAF sensor, idle air control valve, plugs, wires, intake gasket, fuel pressure regulator, throttle body gasket and oil separator. It still ran rough so I took it to a mechanic..he performed a smoke test and found glaring leaks in the intake and oil separator (both fixed now) the car now idles better in park or neutral but around 480-500 in drive or reverse. The idle is uneven, fluctuates and is pretty undrivable. I tried looking for more leaks with starter fluid and I can't find anything. I hear a slight hiss from somewhere but I am out of options. I don't want to buy another part. I am no stranger to Volvo vacuum problems (I've had several) but this has been the most troublesome . Any ideas?

[volvolugnut]

Have you cleaned the throttle body and blade? Set the idle switch on the throttle body (if it has one). Does it have the idle speed control valve used on other Volvos of this era? They get dirty and sticky. Do you have a service manual for guidance? They used to be common in book stores.
volvolugnut