[v8volvo]

Did this only happen one time, or were you able to get it to happen repeatedly under the same conditions? If it only happened once, did you start it back up after stalling it and did it run normally, or try to run away again?

You'll need to figure out if it's running on oil, or on fuel.

If it's running away on oil, you should observe a decreasing oil level and lots of oil everywhere in the intake tract, either coming from the crankcase vent hose or the turbo. If it starts easily both cold *and* warm, and this issue wasn't present before, compression leakage is not the most likely cause.

No on intake or exhaust leaks causing a runaway. If there were a leak on either side you would hear it under boost.

Normal enough for some smoke to come out of the breather and a little bit of oil cap movement when running. To test if the RPM hang is due to an IP issue or oil consumption, you can disconnect the crankcase breather hose and route it into a catch can, and go for a drive... if you replicate the conditions that caused the problem before and it doesn't hang, *and* if your catch can ends up with a lot of oil in it, you've found the issue. If you don't experience both of those outcomes, likely something else.

I've had an IP failure cause loss of engine speed control before so that's not out of the question. If your pump has the kill lever on it, one test is to run a cable into the car attached to the lever so you can pull it if/when the RPM hangs... Just because shutting off the key when it's hung doesn't kill the motor doesn't mean that the issue is not in the IP, when the engine is turning at high speed the shutoff plunger may not be able to stop fuel flow. If you pull the fuel shutoff lever when it's hung and that shuts it down, an IP issue is confirmed. The shutoff lever mechanically moves the control collar so unless something is seriously broken it should always cause fuel injection to cease. Most of the manual trans cars don't have the kill lever, but the early ones ('83 and part '84) seem like they frequently do.