Hello,

Check the front part of the oil pan bottom (may have to go under the car). It should clear the crossmember by 3/8inch to 1/2inch. If not your motor mounts should be replaced.

Check also the ignition circuit - are the plugs still at the proper gap (0.027 to 0.031 inch), the ignition wires securely in place on distributor and on the spark plugs. The distributor and its rotor too - check for excessive wear or pitting.

Another possible overlooked parts are the ignition wires. Estimated life is about 70k km or every 3 years for Bougicord (original part). Non-Bougicord wires may have variable lifespan. Volvo recommends using Bougicord Class F wires (printed on the wires) for higher temp tolerance. Class E (lower tolerance) may also be used nevertheless.

Hope this helps,
Amarin.

I had a car that vibrated sorta like that, although mine was bad enough at times to seriously shake the steering wheel. Over 42,000 miles I chased many things; the list is very long, including 3 sets of motor mounts. Some had some small effect, but none eliminated it entirely. Oh, at times it was not there virtually at all,of course especially when I wanted to show someone and get their opinion.
It was never solved. One person who is Very knowledgable with these motors said he thought it well could be intermediate shaft bearings. These are pretty much NLA,so even if one wanted to,it'd be hard to do.

Bruce/lucid had a problem that he and I communicated about; he had good results with Volvo brand mounts.