My civic has about 65k miles. Not ever driven hard. Trans flush at about 45k. When cold at idle, engine rumbles in every gear except park and drive. It's like something in the trans is trying to bind up. When warm, it goes away, but still does it a bit in reverse.

Any ideas?

 

Dirty idle air control valve or vac leak can cause it. I would lean towards vac leak though as it get better when warm. Does it get rough when you depress the brake pedal when cold/hot as well, try this when i park as well.

 

When cold, it idles idles rough in reverse and neutral. Idles very smooth in park and drive.

When warm, it idles rough in reverse. Idles very smooth in drive, neutral, and park.

I will check for a vacuum leak though. But, if it is a vacuum leak, why would it idle smooth in drive, and rough in reverse?