Today I had a bit of a scary moment on the highway today. I have a 2000 civic 4 door sedan d16y8. I've had the car for 2 years, and I've put about 11K on it (it has 86K now).

When I bought the car in Dec 18, I checked the cruise control, and it worked fine. Probably the next time I used the cruse control was when i took apart the button in Nov 2019 to change the original bulbs for illumination to blue LEDs. The only reason I used it, was to check if it worked (Like everyone checks when they modify something right?)

Today for some ungodly reason, I decided to turn on the cruise. I was going down the highway at about 60mph, and I turned it on. Cars flying past me I decided to accelerate by using the steering wheel "accel" button. Shortly after I reached the 68mph I normally drive at I realized the car was going faster and still accelerating. When I pressed the brakes, I realized I was at WOT because I could tell I had no vacuum going to the brake booster. Things started to get a bit hairy. I was probably going about 80-85mph at this point. I did not want to fry my brakes so I put the car in neutral, and shut off the ignition. I turned on my hazards (engine was off) and I obviously had no power brakes to slow down because the engine was not running. I popped the hood, and actuated the cable by hand, to try and un-stick it, but when I started the car again the rpm shot right up, so I turned the key back off quickly. I disconnected the small vacuum hose that goes to the back of the manifold, and plugged the vacuum leak by sticking the hose on one of the studs. I fiddled with the cable again and started her back up- she idled fine this time.

My question to you is- has anyone had a cruise control stick the throttle wide open like this? I was actually more worried about being stranded and damaging the car than I was about the safety portion of it. I have never taken apart the cruise, but I am researching how it works so I can better understand how to prevent this again. I want the cruise to work, even though I will rarely use it I'm sure.

I've done a lot of work on the car in the last 2 years, so I'm sure I can fix it I just need to better understand where the opportunity for this to stick is coming from. So far I have replaced the timing belt, all new suspension rubber parts and links, changed the power steering rack, changed the fuel lines, gas tank and I've done a ton of electrical modifications. (custom LED dash, backup camera and hid projector retrofit)

I looked for information online for about an hour, it seems that the cable coming from the cruise unit goes back to the gas pedal? Can anyone better explain how the system is supposed to work. I have 3 other cars as well, 1 of which has cruise, but it has throttle by wire and this is my first experience with an old-school mechanical style cruise control.

 

I found a diagram, and I think my vent tube must be plugged. I see how it works, and it looks pretty simple. I will report back with what I find, but if anyone has comments I would love to hear.

 

So I am kind of embarrassed that I asked for help before looking at this myself. The system is very easy to understand as it's operation is pretty basic.

When I got home, I disconnected the soleniod actuator harness and energized these externally with a small 14v power supply. With all 3 solenoids energized I had about 800ma of current draw from the device. I connected the nipple on the cruise actuator to my vacuum hand held pump. I then pumped it up, and it created a vacuum which moved the throttle open. The throttle did not want to return easily when I released the vacuum or when I de-energized the vent or safety solenoid (therefore creating a pressure leak inside of the actuator).

I disconnected the cable from the end of the actuator to determine if my mechanical binding was being created by the cable setup, or the actuator itself. The actuator did not really perform any different. I continued to function the actuator in and out, by creating a vacuum and then releasing it. This made things move more freely.

The actuator now releases fully on its own. The one thing that surprises me was that I expected it to "pop" back quickly when vacuum was released- which it does not. For example if I pump up the actuator with my vacuum pump all the way to the point where it stops the throttle will be at WOT. When I suddenly release it (or open a solenoid) it probably takes about 4 or so seconds to close the throttle completely from WOT to IDLE. It does however return very smooth and steady, which makes me think nothing is binding. I think there may be a little bit of a restriction on the filter side of the diaphragm which keeps debris out of the internals. I did this with the vent hose taken OFF to eliminate any resistance created by the hose. (I did blow through the vent with my mouth, and it was quite clear with no resistance).

I put everything back together today and tested the cruise while paying close attention to it. Things are working as normal. I do notice that if I try and say, set the cruise at 45mph, it will typically set itself at about 47mph once the car reaches "steady state".