In Reply to: Re: Cruise Control lunges posted by Rick Robinson on June 29, 1999 at 00:53:04:
My car also did this, and it is the speedo that causes it. I live in Charlotte NC, but haven't noticed any correlation with weather, maybe I missed it before I got it fixed.
My speedo jumped up as well as down. I could be going <5 mph and it would jump to 50+!!. This is what worked for me:
Cleaned all connections at the sensor (on rear of diff on my '91), and checked wiring. - no change
Removed sensor and resoldered inner connections per a note in the archives - 50% help, but still lunged sometimes - I resigned myself to replacing the sensor.
Changed the diff fluid during routine maintenance, and 'poof' the problem went away. Then, about 5,000 miles later, it started again and is getting worse.
I believe that the metal particles in the diff fluid are at least contributing to the problem, with possibly a weak sensor also. So, I'm going to clean the particles out of the diff possible, and just change the fluid again if not possible to clean them out.
If that doesn't work, I'll try replacing the sensor.
: I believe I know what you are talking about. Next time you are driving on a highway (and there is no around you) spend some time watching your speedo. You may notice that when you car surges, you notice that the speedo needle dips momentarily. If it does, your problem lies in the speed sensor or the cable to the speed sensor. It is located on the front of the diff. The sensor briefly stops sending pulses which makes the computer think you are slowing down, which in turn convinces the cruise control that it needs to speed up.
: That's my 2 cents. (and then some)
: Rick Robinson
: : I have a 1992 auto 525i which began lunging or surging with the cruise control set about two years ago. At first it was only once or twice an hour and they were weak surges. Lately the surges and become severe lunges about twice a minute in hot weather.
: : The car will jump forward for a spit second and then let off only to repeat itself later. It is worse in hot humid weather. I live in North Carolina, USA where the summers can be very hot. I also have a problem with surging under acceleration without cruise control on.
: : Does anyone have any thoughts regarding a solution....and/or a cause?