Hello and welcome to JustAnswer!
Which engine do you have?
Let's see if any fault codes are stored. Cycle the key from off to on three times ending with it on and watch the digital odometer display. Don't crank the starter, just off to on. The codes start with a P and have four numbers, there may be more than one stored. Write down any that you see and post them here.
Sounds great, just let me know whenever you can. Have a great night!
No, it will show up right away. Try it again a few times and you'll get the hang of it.
Get in and close the doors. Put the key in and turn it one click forward, this is off. One click forward of that is on. Start with it off and go on, off, on, off, on and the odometer will change and show codes. REmember to not crank the starter, just off to on.
HERE is a short video I made showing the process.
If it says done then that means there are no codes stored.
The first thing I'll mention is a condition called flashover. This happens when spark takes a path along the outside of the spark plug porcelain so it can't properly fire the plug. This will cause some roughness like you have described and isn't uncommon on this engine. When this happens it will leave a black streak on the plug porcelain and gray streaking on the inside of the plug wire boot. This would require replacement of the spark plugs and wires together. If it's nearing 30,000 miles since the last time the car was tuned up then new plugs and wires are in order either way.
If you have a motor mount that is allowing for excessive movement of the engine and trans it can transmit more engine vibration through the body and feel like the engine is running rough.
These engines also have some normal shake and rough feel to them. If you have had the car for a while you will be familiar with this, but I thought I would mention it.
There are also a few software updates for the engine controller software which may help and idle undershoot problem. If nothing else is found wrong then you may want to have your dealer update the PCM software to the current level and see if that helps.
You're welcome, and good luck with your car!
That's great, I'm glad to hear it. Thanks for the update!