engine sounds like it's only running on three cylinders but I know all plugs are firing and timing is at 12 degrees btdc. Also seems to starve for gas when approaching upper range of engine rpm. Any suggestions out there?
Really a 1988 740 gle wagon on 1990 Volvo 740
Could be the MAF sensor, fuel pressure regulator or something else, hard to know without checking the trouble codes, fuel pressure and a few other things. I suggest you check the codes at pin #2 and #6 on the diagnostic connector, and check the fuel pressure.