My daughter’s 96 Legacy Brighton (MT, 119,000 miles) has been acting up for months now. There are no trouble codes.

I looked at live data with the OBDII reader and noticed Ignition Advance is 14 degrees when the engine is warm and idling. So I Looked at live data from two other Legacies (1995) and their Ignition Advance is 20 degrees when warm and idling. Is this a clue as to what the problem is?

Swapped out the following parts from our 95 Legacy to try and find the fault but nothing helps: MAF, Coolant Temperature Sensor, Knock Sensor, Camshaft Position Sensor, Crankshaft Position Sensor, Fuel pump.

The problem is rather intermittent. Sometimes real bad and other times hardly misbehaves. It stalls out while driving but the engine doesn’t usually die. It jerks etc. It acts like either suddenly there is no fuel or no spark in all cylinders.

Swap the coil.  Had a similar issue on two other cars and in both cases the coil change fixed it.  Don't use an aftermarket one though.

plugs or plug wires?

1 hour ago, 1 Lucky Texan said:

plugs or plug wires?

 

1 hour ago, 1 Lucky Texan said:

plugs or plug wires?

We installed new NGK plugs six months ago. New wires too. 

Swap or test: coil, oxygen sensor, and TPS

But testing will probably be intermittent and only fail if it happens to be currently exhibiting issues. 

(rear O2 sensor isn't used by the ECU for fuel control so you can ignore that).

You've swapped most sensors so might as well swap the rest. 

What exactly does it do:  
how does it start and how long does it last? 
does it restart or have trouble restarting or have trouble driving...?

if it's more common when it's humid/raining/parked over grass/sitting in deep shade - then it's ignition related - coil/wires/plugs

check for a vacuum leak.  ideally when it's having issues. spray appropriate fluid around the engine and see if the idle reacts.

good job pulling some numbers.
i'd guess the ECU is just pulling timing due to poor signals/issues elsewhere and does not tell us much. 
but others will know better and maybe tell you what to look for on that data.

just throwing this into the mix but - kinda wonder about the throttle pos. sensor ?

I had an almost identical situation on a 97 Outback with 2.2 swap.

Ended up being the O2 Sensor.  

I can't find any info from Subaru about how the O2 affects ECU's timing calculations.  But in this one case, for me, the timing was randomly retarding to less 13~15 degrees under light throttle cruising (when it should be more like 20~35)

When the timing would pull back, the car would feel sluggish, no throttle response.  Although for this case it was not a bucking, jerking loss of power.  More like when you get to a slight hill and try to give a little more throttle, nothing would happen for several seconds (timing at ~15)  then would kick in (timing jumps back up to 30 or so) and then acceleration would feel normal again.

Putting in a brand new Denso O2 sensor seems to have stopped that issue and car drives normal now.  Timing stays where it should.