You only need to open the throttle a little as, with the spark plugs removed, there is only one cylinder capable of pulling manifold vacuum - the one with the test gauge screwed in. (and, for the technically nerdy, one of the other cylinders will have its intake valve at least partially open, so there's a big vacuum "leak".) Just stick a coffee stirrer or such into the throttle stop on the throttle cable drum.

It's important to have a good battery and starter motor, so the engine cranks over at a proper RPM.

The main thing is consistency between cylinders. If they are all a bit low compared to a new engine, but close to the same reading, the engine is just seeing a bit of ring wear associated with its mileage. Lots of miles left in it.

If one cylinder is notably lower, it suggests a leaking valve - usually an exhaust valve. In my experience, a leaking valve will give a low reading regardless of how many cranks you use to try to build pressure. In a good cylinder, I see about 75-80% of max pressure achieved on the first stroke and it's 99% all there after the third stroke.

The last check on my 1983 240 (B23F) was at 150k miles and all cylinders were within 10psi of 190psi. That was with MY gauge and MY test procedure. You may well have followed me a minute later and got very different numbers, with your gauge and procedure, but pressures would still be even.

No point in comparing my numbers to yours - the 1983 B23F engines had a higher compression ratio than the B230's.

I agree with trichard - your engine is fine.
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Bob: Son's XC70, my 83 244DL, 89 745 (Chev LT-1 V8), and 2010 XC60. Also '77 MGB and some old motorcycles