Slow to accelerate, wet plugs, fuel in the oil

2017 Toyota Axio. For the past months every once in a while when driving my car will feel like I have to mash harder for it to take off, it will do that for a half an hour or so then back to normal. just recently it was working good then suddenly I heard like a misfire and feel like the car missing when I stop by a light it idles normal but the lights change and I try drive off is like it don't want to move, very very slow until it builds up to a point but not feeling normal at all.. after I when to get it checked everything reads good but showing up a "system lean" we check the air flow sensor, check injectors and still getting the problem after all the attempt starting and revving I notice my plugs got wet and black also seeing some smoke and transparently gas going down in the oil.