I have an 2006 Monte Carlo LT and sometimes when I stop the speedo needle will jump from 0 to 20-30 mph then settle back down to 0 again. It appears to be working fine in every other way it just does this every once and awhile. It happens as soon as the car comes to a full stop. Whats causing this and how easy is it to fix.

 

i've never had the opportunity to work on a 06, but i would assume its the speed sensor on the tranny, it shouldn't be to hard to change.

 

Jeesh, I hope it isn't your tranny.
I had similar symptoms on my 04. Changed BOTH at the same time so I was never able to pinpoint which one it was : MAF and IAC, but the rough idling stop.

BTW, mine went from rough idling, to stalling.

 

it shouldnt be threatening to your tranny, but the sensor is on the transmission.