MC: There is a new write-up you should try before replacing the cable like this article says. CHECK IT HERE

Typically, as these cars get older, certain things start to fail. One such thing is the speedo cable. There is a plastic sleeve in the end of the cable that keeps it spinning in a tight pattern. When the plastic sleeve wears out, the cable wobbles and does not spin smoothly. This causes the speedo needle to bounce. The cruise control uses the speedo signal to regulate the throttle of the car so the speed stays constant. So when the needle is bouncing, the cruise control thinks the car is slowing and speeding up and then surges because it is trying to steady the speed. From experience, I can tell you that this is VERY ANNOYING.

The 88 & 89 Si has a mechanical speedo cable that runs up from the tranny, across the motor, through the firewall and into the instrument cluster. The cable is a 2-piece type. It is usually the upper half of the cable that goes bad and starts to cause the speedo needle to bounce. The upper cable costs about $26 from the Honda stealerships. You only need to buy the upper half. This does not apply to 90 & 91 Si models because the speedo sensor is mounted on the transmission and only wires are run from the sensor to the instrument cluster.

Now installing the new cable is a pain in the ass. To remove the old cable, unscrew the large nut that holds the 2 halves of the cable together. Then remove the cable from all the plastic hooks that hold it in place. You will also want to remove the brake booster hose and the small black bracket that is going to be in the way. From inside the car, you should remove the lower panel beneath the steering column. Then slide the seat all the way back and lay on the floor by the pedals. You should be able to look up and see where the cable goes into the rear of the instrument cluster. A flashlight helps. Most of the time you can just wiggle the cable off but you might need a screwdriver to pry it off. Once it is off, you should tape a small string to the inside end of the cable. Then just pull the cable out from the engine side. The string should go out with it.

Now tape the instrument cluster end of the new cable to the string and try and start the cable through the hole in the firewall. If you have a friend that can pull the string while you try to guide it into the hole, that would help a lot. If not, you will most likely have to run back and forth between the inside of the car and the engine compartment to get the cable through the hole. It is pretty easy to get the cable most of the way through, but getting the rubber seal around the lip of the hole is really difficult. I ended up taking a razor to cut the insulation around the hole. Then I used a pair of needle-nose pliers to pull the rubber seal in through the hole. You have to work it around. Once you get past that, the rest is easy. Just plug the end of the cable into the instrument cluster, secure it with all the plastic clips in the engine compartment and reattach it to the other cable. That should be it. Go for a test drive and the needle should be steady.