Just replaced my pedals on a very old Norco MTB. I noticed while working on it that the whole peddle structure is wiggling from side to side is this normal ? I took the plastic caps off the base to see if it is an easy tightening fix, but not sure if tightening that bolt is the way to correct the problem ?
There could be a couple different issues at work, but it's most likely that the bearings need to be re-greased and/or tightened. On some pedals, that little screw simply holds the pedal body together and the amount of grease in the bearing area will determine how tight the whole assembly holds together.
On the other hand, some pedals have a preload that adjusts how tight the assembly is, simply tightening this might solve your problem.
I would recommend tightening that bolt and see if the problem persists, if not good; if it does, then either replace the pedals or take them in to a shop to take a quick look.
You have a loose bottom bracket (BB). It needs to be replaced.
You need to buy a new bottom bracket along with two special tools: A crank puller and a bottom-bracket tool.
If your current bottom-bracket is cup-and-cone style (it probably is), it can be removed with basic tools and elbow grease. If it's cartridge style, it can be removed with the BB tool.
Here are links to all three at Amazon:
Or, you could take the bike to your LBS and have them handle it. This is a common operation and probably wouldn't cost much.
BTW, the bolts that you see underneath the caps hold the cranks onto the bottom bracket spindle.