2000 s80 misfiring and I just replaced the ignition coils

[AbstractMachine]

To give you some background I purchased a 2000 Volvo S80 T6 a couple a months ago with less than 100,000 miles and the timing belt had been recently replaced, at the time it seemed like it was in great condition, and I knew that there were a few things I would have to tune up on it, but over all in great condition for it's age.

One of the issues I ran into shortly after my purchase was the engine was misfiring. After listening to some advice of a Volvo mechanic and friend, I decided to tackle replacing the ignition coils and spark plugs (I actually used a guide from this site). One thing I noticed while replacing the coils is that every single one of the connections from the wiring harness to the ignition coil had the clip broken off of it that secured it to the engine. The connection fit so snug that at the time this did not seem like a problem.

Fast Forward about three weeks everything was still working great. Then it started again. I bought a diagnostic code scanner that returned the following codes: P0300, P0351, and P0352. Last night, I went back in and used zip ties to secure the connections to the ignition coils.

Today, I was on my commute to work and the same issues started occurring again. The car was rough idling, it had almost no power and shuddered when the gas was applied. When I reached a stopping point I noticed the car had the smell of burning oil, but i didn't notice any smoke coming from the engine bay or the exhaust.

Does anyone have any suggestions of what this could possibly be?

[AbstractMachine]

This issue has been resolved. Apparently the coils that I used were very cheap, and thus were causing the misfire. So, I replaced them with genuine Bosch coils, and everything seems to run fine. For now...