I am not a car guy by any stretch of the imagination, but my wife and I just changed the Ignition Coils on my daughters car. It had been rough idling while braking and the check engine light had come on, so I hooked up an ODB2 reader to it and figure out a cylinder was intermittently missing. It recommended changing the ignition coils, so off to youtube I went to see how hard it was. Turns out it's even easier to do than change a spark plug (you pull the coils out to do that), so I ordered some from Amazon. I priced them locally, but they were about $80 to $90 a piece at autozone and $70 for four on Amazon. Luckily my wife could break the bolts free, to remove them, as my arthritis makes that hard for me. I had bought a 10mm drill socket adapter, just in case, but didn't need it. So yay for saving a few hundred bucks, having a repair shop do it. We found out by reading some posts online, that using Eco driving mode can cause Hyundai Elantras to develop bad coils, so we made sure my daughter understood not to use that mode anymore.