Just to clarify, when testing the coil, it will pop up quickly AND quickly pop back down and that means it’s operating right.....just needs to be coming up fully where it would stop the ball and falling below where it wouldn’t impede the ball. With mine, before I figured out it was wiring that was binding it, it would fire but not fall completely back down or you could hear it firing but would not pop up above the playfield, depending on how the wiring had shifted as I had raised and lowered the playfield trying to troubleshoot. I don’t know that loose wiring is your problem but I had come across that as a solution on a thread here or on rgp and it was what was wrong in my case. If it’s not got wiring binding it, the coil sleeve, plunger or whatever mechs is what I’d check as flynnibus originally suggested