Although the engine light hasn't turn on, lately I have noticed that sometimes while doing lot's of driving around the city and I stop at a red light, the engine feels like it has a semi strong continuous vibration. Then suddenly at the next stop the vibration is gone and it idles really smooth again. Also a couple of times I have noticed that when this has happened and I stop and turn off the ignition the engine almost feels like it fades down as opposed to shutting off right away as soon as the key is turn off. I know I should replace the spark plugs since I don't know when was the last time the previous owner did it. I've only had the car for a little under a month now. Thanks for any input.

 

Keeping the internal engine parts as clean as the outside is often overlooked by many. You should look into the plugs, cleaning TB, MAFS, air filter and using fuel additive to help clean the fuel injectors for better fuel presentation to the cylinders. You can select from many available but I have been use BG 44K for years.

 

Well I don't know if maybe I'm just being overly sensitive about this occasional vibration but at least there's no engine light yet and the car just passed the MA state inspections today. So to me that's good news to know I don't have to replace anything for now

 

The vibration turned out to be the engine fan. That also explains why when it happened and I turned off the engine it still ran for about a second.