Honda Civic 9th Gen. Vibration at Idle?

I'm a proud owner of Honda Civic 2013 (9th Gen) LX 4 door Automatic.
I bought it used for 52 Thousand KM and now it has 72 Thousand KM (20000 in a year)
As a rule I leave the car to warm up in cold mornings, however I started noticing something weird.

In the middle of warming up, The car starts to vibrate the RPM drops whil vibrating, the kind of vibration that would appear just before it stalls.
The car vibrates just for a second or 2 and stops, RPM goes up again and continous to warm up.

I used to feel the same vibration when changing gears (from Drive to Park or Reverse to Park) or turning on the AC, but was very mild, however still can be felt.

Otherwise, when the car is warmed up, it is idling perfectly.

I have already cleaned the throttle body not to long ago, and cleaned the spark plugs as well.
I have took it the dealer ship to advise on the issue, and ofcourse they didn't know what was the issue and decided it was normal!

Any assistance on this regard we be great.

I know that the Civic is still under factory warranty. But when you took it in to have the problem check out, did the R.O (Repair Order) issue from the dealer indicate that any DTC? (Diagnostic Trouble Code). This is a standard procedure when I worked for Honda.

Was the vehicle left there overnight so the technician can or trying to duplicate the complaint in the morning when the engine is in a cold start up or when put the car in gears?

Without the code. It's hard for me to guess, I have to have at least something to go by since I was not with the car to check it myself.

The only TSB (Technical Service Bulletin) I could find relates to the problem is included below and possibly a notice (If it became a recall) has sent to you and it has been done. Hasn't it?

YA has some problem since yesterday and still won't let me upload the TSB. I'll come back and try again. I have to open up the shop. The staff will show up about 30 minutes. I'll be back.

If the car has the defroster on you are still hearing the compressor kick in. Yes even in the winter with the heat all the way up. I agree with the dealer. Normal.
You cleaned your spark plugs. They are probably Iridium and last over 100,000 miles.