On my 2017 accord I noticed when I'm at a stop light my car idles rough and rpms drop a little bit. If I put the parking brake on in drive and take my foot off the brake it idles smooth as can be and the rpms rise up. What is causing this??

 

Brake booster???

 

if your car is under warranty, take it to the dealer to have it fixed. also could be a possible vacume line leak.

 

Is there a way I can test this on my own to see if it is the brake booster? Dealership around here never wanna fix the problem. 🙄

 

Wouldn't try until the dealership has had a look
Talk with tech if possible so you get as much info about the problem

Take off hose on brake booster and plug it.
Run engine and hit brakes to see if same thing happens.
If idle stays the same then brake booster is suspect
If idle does same as before then not the brake booster
But, brake booster is only a guess

 

if you touch anything and leave any hand prints, disturbed dirt / dust on any hose, the dealer will say you tampered with it, therefore you caused the rough idle. make sure you clean any trace of you touching anything under the hood before taking it to the dealer if you touch or remove any lines.

 

So, true.
This is why you should not touch anything until the dealership has had a go at it.
Let them fix it under warranty