What does a diagnostic code 27 on a Dodge Dakota 1992 mean if it is not on continuously?

Power to the pcm was lost or interrupted.Whenever your battery is disconnected to clear fault codes,code 12 remains in the computers memory,the code is erased automatically after 20-100 key on cycles...

Codes on a 1992 should be 2 digit in length.

Nothing. All of the diagnostic codes consist of 2 digits. 'Code 3' must be incomplete.

Codes on a 1992 should be 2 digit in length.

It means there was a fault detected in the MAP (Manifold Absolute Pressure) sensor electrical circuit. The cause may be a loose connection or broken or shorted wiring.