Low idle and poor shifting

Hello,
I have a 94 Mighty Max automatic that we use as a ranch truck. I don't know much about it, so hoping you all can point me in the correct direction. Recently my employee changed the plugs and wires, and then things have gone down hill. The truck starts and runs, but runs at a pretty low idle, so have to keep your foot on the gas to idle up. Also, the truck will no longer go into reverse and seems to want to engage forward in all shifting positions including park. I'm hoping the transmission items are related to the low idle, but not sure.

2 issues:
#1 - low idle
#2 - no reverse

Thank you

I adjusted the throttle cable which took care of #1. For the no reverse, I'm wondering if the Reverse Solenoid in the transmission is bad. Does anyone know how to find that and check it?