This guide will cover the basics of getting a controller setup and working on IW4x, please follow the guide carefully.
As MW2 on PC does not natively support controllers we must use external programs to make a controller emulate keyboard and mouse inputs. This guide will cover using Steams Big Picture mode which has this feature built in.
Step 1: Adding IW4x to your steam library
Launch steam and click the text in the bottom left that says '[+] ADD A GAME'
Select the option 'Add a Non-Steam Game...'
Click the 'Browse' button
In browse file window locate your iw4x install and select 'iw4x.exe' then click the 'Open' button
Now there should be a tick in the box next to iw4x, now simply click the button 'ADD SELECTED PROGRAMS'
Now IW4x has been added to your steam library and can be launched at any time from within Steam
Step 2: Enabling Controller Configuration Support
Connect your controller to your PC via USB or Bluetooth
Open steam and select the 'Big Picture Mode' mode icon (It's located at the top right of the steam window next to minimise)
Once in big picture mode go to Settings (It's the cog icon in the top right)
In settings select the 'Controller Settings' option
Now depending on the controller you are using enable the configuration support, e.g. For an Xbox controller enable 'Xbox Configuration Support'
Step 3: Controller Configuration
Again while in big picture mode go to 'LIBRARY -> GAMES' and locate IW4x, then select it and press 'PLAY' (IW4x will now start as normal)
Once at the main menu, press the (Guide button On xbox controllers) or the (Touchpad on PS4 Controllers). This will open the in-game steam overlay
Select the 'Controller Configuration' option, you will now be presented with a image your controller
Now select the 'BROWSE CONFIGS' button (Xbox Controllers -> X Button) (PS4 Controllers -> SQUARE Button)
You should now be on a list screen of configurations, Go to the 'Community' tab and press the 'SHOW OTHER CONTROLLER TYPES' button (Xbox Controllers -> Y Button) (PS4 Controllers -> TRIANGLE Button)
Now search the list till you find the 'H3X1C's ELITE IW4x Config V2' Configuration, press the (Xbox Controllers -> A Button ) (PS4 Controllers -> CROSS Button) to 'IMPORT CONFIG'
Now You just need to apply the configuration by pressing either (Xbox Controllers -> X Button ) (PS4 Controllers -> SQUARE Button)
Now you will be able to use your controller in-game. I suggest looking at the configuation screen to see how all the buttons are mapped.