Creating IK rig for Mech, but IK Bone Constraint uses bones that I don't want to include

Hello!

I’ve been looking to do an animation with a video game mech, but the model that I have doesn’t currently have an IK rig setup. I wanted to make a quick IK setup to help speed up the animation effort, but I’ve been having trouble getting the bones to move correctly. I am quite new to rigging, and many of the tutorials I’ve watched thus far haven’t been as useful as I thought they would.

Here is a snapshot of the mech I’m attempting to control. The yellow bones came with the model, and while they can be individually controlled like an FK setup, it can be very time consuming to animate motion. Ideally, I’d like to IK rig the arms and legs, but whenever I go to make an IK chain (shift+i), it uses the entire armature as part of the chain rather than just the appendage. The resulting IK disrupts the entire model, and puts it off-kilter. I’m guessing that this can be a straightforward fix, but I’m a bit lost when it comes to rigging. Any advice or links to relevant tutorials would be much appreciated!