Speedo-cruise control issue

[Kamil]

Hi all,
I drove the 535i to Boston from NYC and back again.
I've noticed that at constant speed, my speedometer sometimes (not often) moves (more like "clicks") 5 miles back, and then gets back to the same speed. I've noticed it mostly under constant speed as opposed to accaleration.
Second symptom - when I use the cruise control (not often), I have found that the CC was jerking (almost violently) the car, most often going up a little hill, as it tried to keep constant speed.
I would assume that the two issues and related, and a quick look at bmwe34.net led me to conclude that the speed sensor might be dirty or in need of a replacement.
Can anyone confirm?

BTW - my wipers are fine; I assume that the SS also controls the speed-sensitive wipers, which I don't believe I have; do I?

Thanks for the input,
-Kamil

[Mr Project]

My '91 535i does have the speed-sensitive wipers, but I'm not sure if they were an option or standard.

You can see the output voltage of the speed sensor in real-time via the OBC. Procedures for entering test mode are here:

http://home.iae.nl/users/bts/obc.htm

I think you just need to hit 1000 and 10 simultaneously and then go to function 08. You could watch this voltage reading and see if it fluctuates along with your speedo and/or cruise control.