While there, check the AMM connector plug's prongs for damage. If one or more happens to be bent, very carefully straighten it out. Spray connector with electrical cleaner.

You mentioned the hose from the flame trap to the intake nipple. Make sure the nipple is clear. If you choose to do so, you can carefully remove the brass nipple and clean the area with a small knife or paper clip. Throw away the flame trap screen. It causes more trouble than it's worth. I have driven my 90 244DL and now 95 855 GLT for years without the screen. No issues.

Check ALL vacuum hoses.

If the engine mounts aren't Volvo OEM consider replacing them with OEM to minimize vibration. Volvo OEM mounts are somewhat soft so they will easily shear off in the event of a major accident allowing the engine to drop to the ground instead of in your lap. Aftermark mounts tend to be harder and transfer more vibration.

As Aye Roll mentioned, the lumpy idle is the nature of beast. I could never get my 90 to idle smoothly. There is only so much you can do..:)