Cruise control only works intermittantly - 1999 Audi A8

If the cruise control on your 1997 Buick LeSabre is intermittently working, there are a few potential causes that you can check:

1. Vacuum leaks: The cruise control system on your vehicle uses vacuum to operate, so if there is a leak in the vacuum lines, the system may not work properly. Check for any visible leaks and repair them if necessary.
2. Throttle position sensor: The throttle position sensor (TPS) sends a signal to the cruise control system to tell it the position of the throttle. If the TPS is malfunctioning, the cruise control may not work properly.
3. Servo Motor: The servo motor is responsible for engaging and disengaging the cruise control system. It may be that this motor is faulty or that the gears inside the servo motor have worn out.
4. Speed sensor: The speed sensor sends a signal to the cruise control system to tell it the vehicle's speed. If the sensor is faulty, the cruise control may not work properly
5. Vehicle Speed Control (VSC) module: This module is responsible for controlling the cruise control system. If it's malfunctioning, the cruise control system will not work correctly

It is highly recommended that you take your vehicle to a qualified mechanic to diagnose and repair the issue, as cruise control systems can be complex and require specialized knowledge and equipment to diagnose and repair.

Could be any number of issues? Can you check for applicable trouble codes, relating to cruise control? Some of the national brand autostores will check codes for free.
With intermittent issues, have to do testing when problem is ongoing, or you can't find anything. Do you want to check voltage and ground circuit for your cruise control, meaning, check wire circuits using wiring diagrams?
Intermittent issues can be a pain to track.

worn out possibly or gummed button. Or does it stop working while in cruise control? Does the resume work and accelerate button during operation?

I had this problem it was the switch on the break pedal it would move just enough so the break light did not come on but the cruise would not work

If the speedometer and odometer are not working the problem is usually lack of signal from the transmission speed sensor.
But if the cruise control works and the speedometer does not, my guess would be a problem inside the cluster.

Without testing we'd only be guessing , could be the control module ,electrical input to the control module , switche's etc... don't know what year so can't direct you in any testing proceduers .

cruise control operation is reliant on the following
road speed sensor ( speedo or VSS sensor )
engine rpms tacho/ ignition coil/module problem
clutch pedal sensor (VSS in automatic )
gear selection position sensor ( not properly adjusted causing flickering of the selector light)
brake pedal sensor
bad ground wire connections
r all need to work together or the CC will stop working
nothing to do with vents and all that you mentioned.
wire connections and harness connections for the transmission are suspect
CC will not operate under certain engine rpms and road speed

It is most likely the speed sensor in the transmission.

2005 Avalon only intermittently dedects cars ahead of me.

Faulty product. I install cruise control for 6 years. One of the cables are hooked into the throttle and the other in the vaccuum actuator, since it is electronically controlled actuator, the object itself might be losing it's contents or frankly worded, is taking a nose dive. works much like a brake booster does.

Is it a PID system? (Proportional integral derivative system)
or is it just standard proportional?

That will play a factor.

If you just have one of those cheesy controls (cruise controls), than replace it, obviously it wouldnt of cost much. if it is not, check the actuator and replace it! Replace the Fuse, brush it with wire brush, clean up all connections.
You should be ready to roll!

Good Luck.