Okay so about 5 months ago I put 10W-40 oil in my car by mistake. I drove with it for a little while, but then when it got cold in the evening or early morning my car wouldn't start. The engine tried to stay, but it would just shake a lot. So I changed that right away and it was fine after that.
My recent oil change, the deal i was buying only had 4 quarts of 10W-30, so I used 1 quart of 10W-40. The guy at autozone said it shouldn't be a problem. It's been fine for about 1000 miles so far - a two hour interstate drive immediately followed the oil change.
About a week ago, going up my steep driveway, the engine starting shaking violently again and I had complete loss of power. The engine would barely rev. I got out to look under the hood, and the entire engine was shaking. It slowed quickly until it stopped, and then I was able to drive fine. Today on the interstate, I sped up quickly to about 70. I noticed the tone of my engined changed - it got really deep and gargly sounding. I also had a loss of power, and the check engine light flashed on and off. I slowed down, and it stopped - went about 60, but I could tell the engine tone was deeper and I had less power.I made it home, no CEL right now, but still a deep gargly tone and loss of power. I have a custom SRI which is actually a little bit loose. Could this be the problem (obviously an easy fix which i'm going to do tonight when my engine cools) or is it more likely the oil? or something else?