1st Gen Cruise Control Problem

I have a 1998 that I bought new. Cruise control has never worked properly, but I never bothered fixing it because I never used it. Fast forward 27 years and I’d like to use it. The problem is that the speed is constantly surging and going back down within a few mph of whatever it was set to. Would appreciate any expertise on likely cause of the problem. Thank you,

 

Do you have factory cruise (switch located on the right side of the steering wheel) or dealer installed cruise (switch stub located on the left side of the steering column)? Will help with troubleshooting. I unfortunately do not have the experience to help with.

I have the dealer installed option (Rostra Brand) and it performs as you describe. I am currently acquiring factory cruise parts to add and remove the dealer system.

Hopefully someone can chime in with some helpful troubleshooting advice.

 

Thank you for the feedback. It is on the left side of the steering column. Had no idea this was not factory installed.

 

Yes, that is the dealer installed version. I have the same and it has surged and dropped after setting it since the day I bought the truck in 2001. I have a 99 4Runner with factory. I have finally reached the point to where I want it in the Tacoma.

 

On the throttle body you will see either 2 or 3 cables, 3 cables if she is an automatic. Examine the cable that goes to the throttle pedal first for excessive play, it is easy to adjust. Too loose and you will feel slop in the accelerator pedal. Too tight and you will mess up the adjustemnts of the other cables. If it is fine, leave that one alone. If she is an automatic, slide the rubber boot of the end of the threaded sleeve and look to see if the crimp on the cable is right at the edge of the tube. If this is OK, leave it alone too. Now go to the cable for the cruise control and see how loose it is, it sounds like it is pretty loose. When the cruise control computer senses that an adjustment needs to be made to the trucks speed the actuator has to take up the slack of the cable first and if the computer senses that there is no MPH change, it commands more throttle/less throttle and it adjusts the actuator even more.

The other thing to check is your brake pedal return spring, if it is weak or there is a groove worn in the pedal/mount the brake pedal will jiggle the brake light switch and that will disengage the cruise control constanlty, this same switch will disenage the torque convertor lock up too and that will change RPMs and MPH.