The 380 does not have a lot of off idle power....not for a heavy 107 chassis.
The power issue and idle could well be one and the same.

The vac' system on the early 107's was primarily for emission complience.
By increasing the ignition timing you may run afoul of the smog test numbers....depending where you live. Increase ignition advance does increase the c/o %. It will also impact NOx too.

You need to look very close at the vac' routing and intake/hose condition.
Your's should be too early for the AIR system so it should be simpler to trouble shoot.

To start with....timing is critical to idle quality and stability. If the advance weights are hanging up some times, this will show as an artificial basic timing....when the weights decide to fall back to the normal 'no mechanical advance' position...the engine will tend to stall due to insufficient ignition advance..
This can happen often or rarely.

To check this you need a timing light and be able to pull idle speed down to less than 700 rpm.
The O/T mark and timing degrees stamped into the crank damper are difficult to see with a timing light.....mark them and the pointer with 'White Out' first.

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