So my story is :

I got my car running on one exhaust for like 20 miles in the city and when I realized that engine is bouncing I checked the car and one of the exhaust was blocked with ice. I broke the ice ( took 1 hour) and drove it to my home. Next morning I got sweet engine light And my mechanic gave me the code p0170 and change the spark plugs and there was oil in one of the spark plugs at the front. The light was them gone and I drove the car and on my mechanic advice I put the fuel injector cleaner . Next day the light came back and it was on for 2 day then after 2nd day of light 3rd evening light went off and stayed of for 1 day and the 4th day light is again on. Engine on idle is bouncing the car a little and rpm is going below 1000 to 400. When car is running it take more power to shift gears . I don't know what is wrong as my mechanic is now tired of my calls and saying that my car engine needs to be replaced .... Awkward he is or do I need to replace the engine . He is also saying one of the piston in engine is throwing oil in the sparks plug and making them not to work that causes less power for car and this is happening... Any advice ???