Does this sound like starter or ignition switch issue?
 

My 81 930 has two new symptoms when trying to start. Normally when I would turn the key, the car would start and then I could release the key. Now, occasionally, I will turn the key and engine turns and turns but only starts after I release the key. Other occasions it acts like battery is very weak, engine barely turns. After several attempts it will come back alive just enough to start the car. After this, I could turn car off and it would start and behave normally for several days or longer. I can’t figure out if I need ignition switch looked at or starter. The battery has been checked several times.

Is the starter cranking the engine at a decent rpm? If so, I doubt the problem is with the starter. Really odd the engine starts on release of the key, I would start there.

As I said most of the time the starter cranks normal speed. However sometimes it behaves like the battery is weak (turns very slowly or barely or not at all). After a few attempts it might crank faster and start. Then the next time around it cranks full speed and starts on a dime normally. Having to release the key is also not consistent. Sometimes it will start only when I release. Other times it starts normally, but I do feel releasing the key is more required when the cranking is slower.

Engine starting after the key returns from the start position to the run position MIGHT be the contacts in the ignition switch.
Slow/different/intermittent starter operation can be a number of things.
First place to start is battery connections including the negative chassis connection, the ground strap under the transaxle, and all the ground points.
A bad battery wire connection on the starter can produce the same problems you are experiencing.

I’m trying to study the wiring diagrams and can’t tell how the ignition switch and starter solenoid are connected. Is there a relay in between, or does the power from ignition switch go directly to solenoid on the starter?

I can't get to my wiring diags right now for the 930. A few days away, if no one else chimes in. But I don't think any other relay. The relay is the solenoid. From memory.
But what you describe with engine firing just after starter disconnected is often battery condition. It is so far drawn down for starter crank load (3-400amps) there is nothing left for the ignition spark. Once you release that load if it has enough residual crank speed it may just fire in time.
Try swapping another temp battery or jumper another one in.
Alan

I think you are right about the battery load but I’ve checked the battery multiple times. I think it has to be the wiring from battery to the starter or ground. I’ve checked at the connection points and they seem ok, and the fact that is not consistent is making it hard to diagnose.