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Wandering cruise control V70-XC70 1998

posted by KlausC on Thu Mar 20 11:21 CST 2008
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last visit: Fri Oct 24 10:15 CST 2014

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My cruise control has started to act up. It works, but it doesn't hold the speed very well. It will fluctuate 5mph down from where it was set and then very slowly get back up to speed, and then loose it again. Really frustrating on the Interstates after passing someone and then slowing down.

It is also very slow to respond to resume, I count a full 5 seconds before the CC acknowledges that I hit resume. And then it goes very slowly back to the speed set.

It is not so bad at high rpms, like 3rd gear at 65. I did look at the vacuum lines at the CC motor and no problems with cracking or leaking. I did replace a few elbows at the intake manifold, but same old problem.

Any hints? Been there, done that???

Thanks,

Klaus
--
The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

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Wandering cruise control V70-XC70 1998

posted by TomL on Thu Mar 20 17:10 CST 2008
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last visit: Sun Jul 25 18:24 CST 2010

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Klaus,
The problem could still be the CC vacuum line or the switch at the brake peddle. If you have a hand vacuum pump, connect it to the line at the pump and apply vacuum. The throttle should respond to high vacuum and hold there until you release it or press the brake. If you can't get it to actuate the throttle or it slowly losses vacuum than there is a leak someplace. The CC is totally independent of the engine vacuum. You could also have a pump that's going south.
--
Tom 69-1800S, 72-1800ES, 96-850T,2000-S70 GLT-SE

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Wandering cruise control, replaced switch V70-XC70 1998

posted by KlausC on Mon Mar 24 09:10 CST 2008
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last visit: Fri Oct 24 10:15 CST 2014

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I replaced the switch at the brake pedal and all is back to normal. The vacuum leak was internal to the switch.
Now I get to take it apart to see how it works!!! :)

Klaus
--
The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

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Wandering cruise control, replaced switch V70-XC70 1998

posted by TomL on Mon Mar 24 13:55 CST 2008
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last visit: Sun Jul 25 18:24 CST 2010

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Good show! I always do that too.
--
Tom 69-1800S, 72-1800ES, 96-850T,2000-S70 GLT-SE

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Wandering cruise control V70-XC70 1998

posted by KlausC on Fri Mar 21 08:50 CST 2008
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last visit: Fri Oct 24 10:15 CST 2014

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Thanks Tom,
I now have a second excuse to get a Mity Mac!! After re-reading the 850 online diagnostics, you are very correct. A slow vacuum leak is the most probable cause.
After this last 6 inches of wet snow get cleared, I will test the vacuum pressure at the brake switch end and see if the bellows pulls the gas pedal forward and holds it. Probably an old, worn out switch. I hope.
I just don't like pulling the battery out of the car when I can help it!!

Klaus
--
The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

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Wandering cruise control V70-XC70 1998

posted by dick on Thu Mar 20 15:18 CST 2008
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last visit: Sun Aug 3 15:24 CST 2014

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My 98 S 70 T5 is a slow responder but not that bad. I did replace the electrical part under the hood with a good used one. Guess it is a relay or whatever it is called. This seemed to help, but it is not as quick as my wife's 91 940 SE or my 940 T.

dick

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Wandering cruise control V70-XC70 1998

posted by KlausC on Thu Mar 20 17:02 CST 2008
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last visit: Fri Oct 24 10:15 CST 2014

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I just remembered... this started to happen after I R&R'd the intake manifold doing the oil separator stuff. I wonder if I got a vacuum line wrong or didn't spool the throttle cable correctly???

It is like the CC is not responding fast enough to keep the speed even.

Klaus
--
The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

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Wandering cruise control V70-XC70 1998

posted by rhaire on Thu Mar 20 12:25 CST 2008
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last visit: Mon Aug 4 10:16 CST 2014

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I have no great insight into this one. The cruise relay flaking?

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Wandering cruise control V70-XC70 1998

posted by KlausC on Thu Mar 20 13:57 CST 2008
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last visit: Fri Oct 24 10:15 CST 2014

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Robert,
Thanks, I needed that! I was thinking vacuum and forgot all about the dumb relays. I guess I will have to trouble shoot them as well.

Klaus
--
The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

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