I agree with Bob 100%. Sparks almost have to be a problem with either the plugs or the wires. If you don't know the age of the parts, replace them. Bosch or NGK plugs, Bougicord wires.
As for the sound, we too had a loud mystery clicking/ticking/clacking sound in our 1991 740. Very strange timing, seemed to slow for the bottom end, not rattly enough for the top end. I thought it was a bad or poorly adjusted valve... with 300K miles on it, very possible... until I read somewhere that bad exhaust manifold gaskets can cause a funny ticking sound. A superficial examination showed the exhaust gaskets in not the greatest shape. I figured it was worth a try, so I got new gaskets, pulled the manifold off to find the gaskets were truly toast. We're talking a millimeter or two left between the outside and inside. I replaced everything with new gaskets, and the car runs and sounds like new again!
If you do get new gaskets, avoid ScanTech. I'd say Elring or dealership band only.
Good luck!
-Ryan
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Athens, Ohio 1987 245 DL 314k, Dog-mobile 1990 245 DL 134k M47, E-codes, GT Sway Bars 1991 745 GL 295k, Regina, 23/21mm Turbo Sway Bars Buckeye Volvo Club
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