MAP Sensor error
 

1988 c1500 Silverado. 5.7
I am getting several codes related to the MAP sensor (open or shorted) think it was code 34.
Thought I erased it and others but comes right back on scanner. Any way to ohm out before I waste money on MAP. Has three wire connector. Also getting electronic timing control error. Says possibly related to MAP.
All are original parts.
I read to disconnect battery for 20 seconds to erase codes. is this correct?
Scanner says disconnect fuse or battery.


Dan