That game uses a solenoid expander to power some of the coils including the outhole kicker. It's possible that is malfunctioning. Look under the playfield for a small rectangular board with a relay soldered to it. There should also be a dummy trigger bulb next to it. Put the game in lamp test and you should see the lamp flashing and hear the SE board relay clicking like a car's turn signal. If it sounds erratic make sure the dummy bulb is good and has not been removed or replaced with an LED. Then I would remove the SE and resolder its connections on the back.
As a last resort I would bite the bullet and buy a new coil and sleeve.