Feriofan

I left my car sitting for like a week, when I decided to start it and let it warm up I noticed that when it cranked the Speedometer jumped to like 40mph… I decided to let it go and to think that was just my imagination since it only did it once.

Next week I was getting out of work and when idling in the parking lot it started to do this again now was at least 5 times, just jumping from 0 to 40mph when the car is standing in the same spot???
I went home and decided to clean the battery terminals and check all the fuses in the car, all of them seem ok.

The car went fine for a couple of days and this morning started to do it again??? I also noticed that this only happens when the temperature outside is fairly cold and only when you start the car for the first time..

Anyone had a problem like this, or any opinions of what should I check???
Also noticed that my engine goes down like 500rpm every time that I’m at a stop light pressing the brake pedal

Any help will be appreciated