My 1991 940 SE Turbo began ticking or tapping at 65 mph when cruising with light throttle. When I accelerated the noise seemed to go away. I didn't hear it at other speeds but it might have been masked or just acoustically enhanced at that mph. First I thought it was a sticky lifter so I changed the oil after a cleaning additive and used 10-40 synthetic. No change. I thought it might be an exhaust gasket leak but I tightened the nuts to the exhaust manifold and no change.
Finally I ordered the IPD valve shim kit since this motor had about 150K after I installed it. I already had the valve depressor tool. Two valves were .0435 so I corrected them to .040. One was .053 and I corrected that to .040.
They were all intake valves.
Happy to say that corrected the annoying and worrisome tapping and she sounds much better even a tad peppier.
The motor never did lose power or get squirrelly, buy I am glad I remedied the symptom. People say the engine is a bit noisy but in this case the noise is correctable and I recommend it. Rental of the shim kit is $40 plus shipping back and forth.