Hello! I have a gen 3 Montero (full size). The C/D light was flashing so I replaced the free clutch valve solenoid (I bought a cheap one from amazon). It did. Help the C/D orange light flashing but now the front wheel lights flash when I put it in 4H. They flash for a long time and then finally engage. If I leave it in 4H after it engages, it will stay engaged with no problem. Could this be because I bought a cheap solenoid? Or is it another issue. Any help would be lovely thank you!

 

So it sounds like you're able to go into 4Hi but it takes a while, right?
I don't think it's because you bought a solenoid off amazon.

This is what helped me with the same problem:
1. make sure the vacuum hose on the back of the plenum that goes to the solenoid is connected. actually check all the vacuum lines related to the frond diff actuation system (the ones before and after the solenoid you bought) to make sure the system can hold a vacuum / isn't leaking air.
2. remove the front skid plate. undo one end of the bellows that covers the front diff freewheel clutch actuator (the arm that engages the front half-shaft). clean and lube the actuator and put the bellows back into place.
3. "exercise" the actuator by engaging 4hi a few times per week

This isn't super hi-tech advance, but hopefully it gives you a place to start. Good luck!