I've been having a hunting idle problem now for what seems like decades (ok it's a 91) and never checked this before.

The regina systems use a MAP sensor. The faq's say "Regina Manifold Air Pressure (MAP) Sensor. The Regina fuel injection system uses air pressure and temperature in the intake system to compute the air mass moving into the engine. The MAP pressure sensor is located on the driver's strut tower support. It is connected to the intake manifold through a hose and takes a reading of intake pressure. The sensor is piezo-electric and changes a voltage input to an output signal proportional to manifold pressure. The system calibrates atmospheric pressure when the engine is started and under full load conditions."

Well if the Vacuum line running to it gets fouled from the intake manifold/throttle body, your system will idle like crap.

Make sure you have no leaks, but also make sure you do not have reduced vacuum due to a semi-clogged line.

Credit goes to CRISSIJ
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1991 740 B230F 135K miles