KJet is sensitive mostly to incorrect fuel pressures and vac leaks. I'd take a close look at your air duct between the fuel distributor and the engine and then all the smaller vsc hoses and manifold and just confirm nothing has a split or has come loose or something. You'd then want to test fuel pressures but it takes a bit of doing.
If you go to Oz Volvo's archive (https://ozvolvo.org/archive/) and search "K-Jet" you will find some service manuals that have diagnostic procedures for KJet, which may also be helpful.