Out of control cruise control

[philx]

I purchased a 87 Monte Carlo SS this week and when trying the cruise control when you engage it, the car shifts down and goes to 75MPH then shifts back up You can turn it off with the switch or hitting the brake but it seems be to stuck It will keep it at 75 on the open highway up and down hills Anyone have any ideas . I have checked vacuum lines wires etc but have no clue what is going on

 

[David.C]

I purchased a 87 Monte Carlo SS this week and when trying the cruise control when you engage it, the car shifts down and goes to 75MPH then shifts back up You can turn it off with the switch or hitting the brake but it seems be to stuck It will keep it at 75 on the open highway up and down hills Anyone have any ideas . I have checked vacuum lines wires etc but have no clue what is going on

I would start with the Cruse control transducer (mounted under hood w/ 2 speedometer cables going in to it) then both cables, then speedo gears.

 

[pontiacgp]

I purchased a 87 Monte Carlo SS this week and when trying the cruise control when you engage it, the car shifts down and goes to 75MPH then shifts back up You can turn it off with the switch or hitting the brake but it seems be to stuck It will keep it at 75 on the open highway up and down hills Anyone have any ideas . I have checked vacuum lines wires etc but have no clue what is going on

that's not a Monte Carlo SS, it's a Tesla....

 

[fleming442]

*Toyota/Lexus