Other than those typical things that you've probably looked at (PVC, IAC, air filter cleaning, Throttle body cleaning, manifold cleaning, etc.) there's not much I can think of. I'd put the typical engine cleaning liquids into the various fluids of your car. Things such as Fuel Injector Cleaner in your gas tank, Carbon remover in your oil, that kinda thing. I know that I use a product called BG44 every few months or so that really cleans out the engine well. It's a bit pricey ($15 for a little can) and I don't know if you have it in Canada, as it's hard to find even here in CO, but it's great stuff, and I'd at least do it to clean your engine, even if it doesnt yield the results you need. Try it alongside some fuel injector cleaner, maybe that will do the trick.
