I feel your frustration with the intermittent cruise control issue. I have replaced my cruise control switch and that didn't help. I have done the same vacuum test that you have and it worked fine. I have checked the vacuum pump by plugging in three leads and checking for any voltage across the leads. There was no voltage so I am assuming that the pump is not the problem. I thought it could be a bad connection or broken wire but it is unlikely that we are all suffering from the exact symptoms due to this. I am currently leaning toward replacing the controller next.

 

Jeff-

It seems every two weeks you post this problem, I've looked at it before, but have never come up with anything.

Two ideas:

1. Go into the electronics box where the cruise control brain is under the right side cover in the engine compartment, it's the silver box on the right of the 214 relay that is shown in this picture.

<img src="http://www.audipages.com/Tech_Articles/auto_transmission/tip29.JPG">

Unplug the electrical connector and plug it back in again, make sure nothing looks fishy.

2. Did you check the brake vacuum bleeder valve?

This is what the Bently says to do:

Cruise control vacuum system, checking for leaks

- Remove vacuum hose from vacuum pump and plug hose.

- Remove driver's side instrument panel trim.

- Push in actuator diaphragm and at the same time push brake pedal down to point of resistance.

- Release brake pedal.

- The actuator diaphragm must not move.

Note:

Incorrectly installed vent valves, leaking actuators or cracks in vacuum hoses can lead to malfunctions.

One last thing to give to you is a picture of the vacuum pump from the front wheel well. I replaced my inner fender on the driver's side and snapped a few pictures, here it is. It's from the wheel well looking forward:

<img src="http://www.audipages.com/Tech_Articles/electrical_equipment/ccontrol1.JPG">

I have not yet had any problems with my cruise....knock on wood.

pw

 

I am looking for an old/replaced A8 cruise control stalk switch. I want to take it apart to see if some of my intermittant problems can be cured by using stabilant 22 to make better electrical contact. I may have the same unresolved issue as you do.

 

Paul,

At this point I am only posting this information so other people know what I have tried without success so they don't spend money on parts that may not be necessary. This problem is becoming very prevalent and has exactly the same symptoms for everyone. I believe that when I, or someone else, find the solution to this common problem we will all benefit.

I have done the vacuum test as per Bentley and it passed without any problem so I can rule out vacuum leaks. I have not replaced any vacuum valves and it worked flawlessly until about two months ago so incorrectly installed vacuum valves is not a possibility. I have tested the vacuum pump for voltage readings and when the cruise isn't working there is no current going to the pump so I don't think it is the pump. I have tested the electrical switch at the brake pedal and it works fine also.

I located the controller a couple of weeks ago and unplugged it and plugged it in again to make sure it wasn't a bad connection but that didn't help the problem either. I plan to take the controller out again and take the cover off and see what is inside since at this point I think the problem is in this box and I don't have anything to lose.

Jeff B

 

Steve,

I have the switch but I have used contact cleaner on it and finally replaced the switch without any improvement in the symptoms. You may want to read my post below, "What I have done so far and what is next to try", before you do anything with the cruise control switch.

Jeff B

 

I thought I would experiment with the switch first. I wanted an old one to take apart before I touched mine. There is a product called Staballent 22 (or something spelled close) that I have seen used on balky switches to improve/cure problems with faulty contacts.

 

I have the same problem and I'm going through the same steps on my 1998 A8. :-(

Please keep posting anything you find/try on this topic. It is greatly appreciated.

 

I'm suffering the same problem as you all. I just replaced the control switch on the steering column which brought things back to intermittent. I assume all the vaccuum lines and the pump are in good order, although I could check, because when my cruise does work it works perfectly. I'm leaning towards getting a used computer from a junkyard.

 

Same thing here - When it works, it works perfectly. I'd say it's about 25% of the time that it does engage.

I didn't see any follow-up posts on this... wonder what people ended up doing?

 

I'm new to the Audi forums... just discovered the others. I'm going to try this and return and report if it worked.

http://forums.quattroworld.com/a8/th...96.phtml#19665