1998 740 turbo w/185K miles. Need a little diagnostic help. This\nproblem came on very quickly. I can't be sure but somehow I think it\nis related to possibly a tank of bad gas. Then again, it may have\nbeen developing for a long time and may simply be age. Owned car\nsince new. Changed oil and filter every 4K.\n\nCar always starts, stalls a few times then is OK. (in winter it\ndoesn't stall) Lately, very very rough idle as opposed to normal\nrough idle. Also stalls and stumbles at idle. Never a problem\nre-starting. Lately, no or very little power below 3,000 then most of\nthe power returns till 4,500 or so, then peaks. Also hear a slight\nbackfire/stumble when at idle and I blip the throttle. Gas mileage is\nworst ever.\n\nAdded techron several tanks ago. Didn't really help. Tried again,\nstill no real help.\n\nHad annoying little oil leak (one of many over the years)which I\ntraced to either the valve cover gasket or cam shaft seal. Replaced\ngasket and now get lots more oil dripping onto water pump and being\nblown everywhere by the fan.\n\nPulled intake hose off turbo and found very slight lateral movement\nwith almost no axial movement. I could spin turbo with my fingers.\nExpected little or no friction and it to just continue spinning, but\nit didn't.\n\nChecked fuel injectors, ballast resistor pack, temp sensor, knock\nsensor, air valve, throttle switch, AMM. All tested good per Volvo\nservice manual. Plugs (platinum) all were uniform in light color. No\nsigns of oil. Replaced dist. cap, tested wires, replaced air filter.\nchecked hoses for air leaks.\n\nAt this point in time I suspect either the catalytic converter\n(original) or the AMM. I doubt I can get the bolt out of the header\npipe (also original)to test the pressure and I hate like hell to start\nreplacing parts considering the 185K miles.\n\nOne other observation. Over the past several months I did notice that\nunder heavy accelleration the boost gauge readings were kind of\nsluggish. Any thoughts?