Suggest you go to VClassics.com look in the technical archive for an extensive discussion of the D jet fuel injection. With the article, a volt/ohm meter and a few hand tools, you can trouble shoot all the sensors, wiring, fuel pressure regulator etc. Then replace anything that doesnt check out. Also, VCOA sells a book on Bosch Fuel injection systems written by Charles Probst. The L and LH jetronic, which replaced D jetronic, is a main focus of discussion on pulsed injection followed by discussion of differences between it and D jet. Extremely useful and logical troubleshooting approach.

If you decide to pull the fuel rail and injectors, which is not hard to do, and you find them really gummed up, here is the method I used to clean them. Remove the injectors from the fuel rail. Run a piece of fuel line from a small windshield washer pump(one you will not use for anything else) to the injector inlet. Run another piece from the pump to a coffee can filled with injector cleaner. Attach a 1.5 volt flashlight battery (no more voltage or you will burn out the injector solenoid) through a momentary contact switch to the injector electrical contacts. Point the injector at an empty coffee can, turn on the washer pump (I used a 12 volt DC model train transformer as a power source; you could also use the car battery) and start pulsing the injector. Keep at it until you get a nice even fan shaped mist.

As far as brake calipers go, check the rubber boots around the pistons. If ripped or missing, eventually, the calipers will begin to stick. On the front, Volvo used both ATE and Girling. If your car has ATE front calipers, and you need to replace one, consider replacing the pair with Girling. Changing brands, in pairs is OK. For whatever reason, you can get refurbished Girling but not ATE calipers from Volvo. I am unsure if Volvo used both brands in the rear, but the same swap out applies, depending on availability of refurbished calipers.