Cruise control won't hold speed.. What to check?
 

If you set it at say 85, it will engage, hold speed for a min, then slowly start dropping.

The cancel button works, so does the resume.

Thoughts?



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It will drop about 3 mph. I always set mine 3 mph more than where I want it to sit.

Now if it keeps dropping, check for a cracked vacuum line at the servo in the engine bay, the skinny one on top of it, the thicker one is the breather ( could be cloth wrapped if not replaced by PO ) hose.

Very, very, very common problem on this forum. After thirty plus years the Cruise Cntrl module gets tired. LOL Actually, could be a capacitor or two gone bad on the CC brain module along with a few bad solder joints on the PC board. There used to be a guy who repaired them on Ebay for $80, he still offers the fix but has jacked up his price to $190. A price I consider ludicrous!
911 928 Porsche Cruise Control Computer Repair Service to Your Unit 92861712700 | eBay

If you search on this forum you will find a couple of folks who found a source for repair a lot cheaper, but it's hit or miss. You will most likely get a lot of other suggestions to try to fix this problem, but believe me, IT'S THE CC MODULE!!

UPDATE EDIT: check this post for CC module repair service some Pelicans have used successfully
http://forums.pelicanparts.com/porsche-911-technical-forum/851491-new-cruise-control-repair-guy-block.html

Hi. A few years ago my speed control did the very same thing. I bought a used module on Ebay for $65 and it is all fixed now. Easy to remove, easy to install.

Yes, I too have bought several used modules off Ebay and Pelican, but they mostly were
partially or completly inoperable. Definately a crapshoot! I have since repaired the bad ones. I would recommend the OP try the MBENZ repair guy in the thread I linked to.

http://forums.pelicanparts.com/porsche-911-technical-forum/851491-new-cruise-control-repair-guy-block.html

Yeah, unfortunately mine keeps decelerating. I could live with it I suppose, but I'd rather get it working if possible. I plan on doing some lengthy trips in the car and it's nice to give the right foot a rest.

I'll check out the new guy.

Appreciate all the help!

If you get a good fix result from the MBenz guy, be sure and report back on this thread
so we'll know if this guy is viable or not.
Good luck.

I emailed him today and still haven't heard back. Will keep you guys posted for sure. Hopefully it works out with him as the price seems fair.

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You can always call Pelican Parts customer service and ask (phones still work these days) them if they have
a supplier who rebuilds cruise controls or can recommend one. Pelican Parts has many vendors not listed in their catalog.

When you turn on your cruise control, do the windshield wipers start going?

If so, either you are using the wrong lever or you don't have cruise... SmileWavy

Damn, you nailed it lol. I wondering why it kept slowing down and the wipers were running :)

Got an email from him this morning. Seems like a nice guy.

Price went up a bit... It's now $80 plus $8 return shipping.

Seems reasonable compared to the ebay guy. My tech is pulling the module next thurs while he's installing a new squirter pump, so I guess I'll give this guy a try. Seems to have a solid reputation and experience doing this.

I'll let you guys know how it works out.

This is the message I got this morning when I inquired if he was still repairing porsche modules:

I do! I would be happy to help out. Go ahead and send the unit to my address on the attached form. Amplifier repair cost is $80 plus $8 for return shipping cost.

My preferred method
 

The way I like to fix the cruise control is, check and see if it's connected. If it is. Disconnect it.

No idea why these cars have cruise control.

I drove for 3 hours on the interstate Sunday night. That's why :-)

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These folks repaired mine and did a great job. Lifetime warranty and inexpensive. http://forums.pelicanparts.com/porsche-911-technical-forum/882999-cruise-control-repair-new-source-under-100-a.html. http://www.autoecu.com

I tried the Mercedes guy for over a month with no reply, he either died or retired.


Just used the module again this weekend when crossing 2 hours of high desert in answer to the fish guy. Remind me to not call you if my house is on fire, since your advice would either be 'get out' or 'never buy a house'. Very helpful.

Interesting issue...perhaps it's my driving style, but cruise control actually being used in a 911 never occured to me.

Do you do any interstate driving where you drone on at 80mph for hours at a time? :-)

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I believe this is the same guy in referenced in my post. Kris from cruise control repair dot com?

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Deputy, please keep us posted on the repair, very curious if it was the servo or module.

You may not do 10 to 12 hour long hauls on highways and interstates where making good time is paramount. When not doing 600 miles in a day, it's the back roads and twisties where cruise is never a thought.