Fuel Pressure Regulator "leaking"?

[schrocketeer]

When I spray carb cleaner around the Fuel Pressure Regulator on my '86 K100, it runs smoother and accelerates cleanly. "Normal" starting idle with carb cleaner. Holds a steady RPMs for a given throttle, as long as I keep spraying.

Without carb cleaner, engine revs only build up with throttle opening surging (open/close, open/close, quickly repeatedly). Starts consistently at a very low idle. Took on a 5 mile test ride. Had to feather the clutch and blip the throttle. Will not maintain steady RPM for a given throttle.

Removing/re-installing smaller line off cylinder #4 vacuum in to pressure regulator makes no change to this condition.

Current Regulator opens around 36 psi. Photo shows last night's test: regulated air compressor in to line off fuel rail return. Bore scope showing (and separately hearing) bubbles as the regulator opens and returns fuel in to the tank through the check valve.

Before I replace the Regulator, does this behavior sound like the Regulator is the source?

In the last month: new fuel lines in/out of the Regulator. New coolant sensor, Hall effect sensor. Swapped in spare Throttle Position Sensor (set to "click"). Fresh Ethanol free, 93 Octane fuel. New NAPA fuel filter.

[Laitch]

Is there moisture or the odor of fuel coming from the fuel pressure regulator vacuum line?

[schrocketeer]

No odor or moisture from the Regulator area.

BTW, also new Intake Boots installed this weekend.

Curious what could be positively affected because I'm spraying carb cleaner in that area.
Grabbing at straws here, trying to get my Brick back to fully functioning.

Before I pulled it down for Coolant Sensor, then Throttle Position Sensor, then Intake Boots, I'm not sure what's left to check?

The only reason I started installing parts was hard, hot starting. Other than that it was running great. Not sure what failed, or I bumped/messed with, installing these parts?

[schrocketeer]

Replaced the Fuel Pressure Regulator, and the fuel pump, and the smaller vacuum line from the bottom of the Regulator in to Cylinder #4. Also cleaned the pre-screen on the fuel pump.
Attached photo shows I checked for housing leaks in the 3 Fuel Pressure Regulators I have.