i got to my car running this morning and everything was fine, i went to my boy's house to install a 3-step launch control everything was fine(still) when we got done with the 3-step and drove the car i notice the needle bouncing from 0-80 then back down to 20 then 40 and so on and so on. pulling my hair off!! any ideas??

 

top for i get some dinner.

 

Where did you get power and ground for the 3-step from? Did you tie in to the power for the speed sensor or something? Maybe the ground is not proper on the side of the coolant housing. I would go over all your connects and make sure that they are solid.