Possible decel valve problem, Idle likes to drop to zero after warmed up. Options

[boxsterfan]

1974 2.0L D-Jet

Once the engine gets warmed up, my engine RPM likes to drop down to zero when letting off the gas. This is not just a "gauge" bouncing issue but rather you can feel that the motor has dropped to zero (stalling).

Does this sound like a condition that can occur because of a faulty decel valve? Anyone in San Ramon, CA have a known working spare one i could test with?

Part#: U039133551
Referred to affectionately as a decel valve, this factory installed device lets the idle down slowly to more effectively limit the unburned gas exiting the tail pipe and keep the engine from stalling. mounts on the right side of the firewall just above the pressure sensor and just behind the battery and three vacuum lines attach to it.

[r_towle]

Remove and plug the AAR, decel! and all other vacuum lines! including the vacuum advance to the distributor.
Leave only the MPS plugged into the plenum.

Then troubleshoot.
Do valves, dwell and timing
Check the TPS to verify it's set properly
Check fuel pressure
Check your CHT resistance cold and hot.

Then add only one vacuum system at a time
If the car runs fine without any new vacuum systems, you will find the culprit.

Tune up the car first or you will waste a lot of time.