Wiper Info
>The car has a problem that has been growing worse over a long
>time: when the windscreen wipers are in the lowest speed (when
>they make a sweep once about every 5-10 seconds) or when doing
>a single sweep they move in jerks. When they are in continuous
>or fast continuous they work ok. A couple of days ago I took
>the big wiper/washer relay apart and sprayed contact cleaner
>on the relays. Then it worked ok for a about a day...
>I find this very annoying since it is just in front of my
>eyes, where I want to see BMW quality... 
>Has this happened to somebody else? What can i do to fix it?
>I don't want to change the big relay since i have heard that
>it is > 100 $!
>Oh, by the way, interesting point: the big relay contained three
>relays AND a 4-bit micro controller: a small 4-bit processor with
>about 500 bytes ROM and about 32 bytes RAM (NOT kilobytes...)!!!
>'85 318i
Subject: Re: Jerky Wipers 
Right church, wrong pew. The problem is in the wiper motor. There are
two contacts in there to tell the system when the wipers are "at rest".
Grease from the gears inside the housing gets on the contacts. This is
a very easy fix if the motor is easy to extract from the car (on my '83
5 series it is not but on my "new" 6 series it is!).
When I cleaned mine the first time I tried to put some of the excess
grease back on the gears - WRONG! Within a month I was back re-doing
the job.
I too spent "hours" fiddling with the relay, including buying a new one
($$$$) to no avail. If only I had known (or been on this board!!!).
Rolf.. AH! HA! A problem I am INTIMATELY familiar with! I had exactly the 
same symptoms.. and went the same route troubleshooting it..
Your wiper motor has a bit too much grease in it and it has
hardened up on the "park" contacts in it. Sounds complicated,
but it's actually (as far as BMW's go) not TOO hard to fix.
The story is: the wiper motor has contacts in it that make it
continue to run, and park. These contacts close on a metal
segment on the plastic gear that drives the shaft coming out of the
motor (the motor itself is at right angles to this). If the
housing had too much grease in it (which was fairly common,
at least on my year), or the grease has hardened up.. the contact
tend to skip a bit, causing the jerky action. The big hint is
that it only occurs in the intermittent mode (which you describe).
TO FIX (Two choices):
1. Go to dealer, sell left arm, buy new motor.
2. Remove motor and clean out grease, regrease.
Assuming you may want to tackle #2.. here is how it's done:
1. Remove the motor. I'd disconnect the power connector going to
it first (it will try to park otherwise if you accidentally rotate it,
perhaps taking a finger or two with it). On my 535 - it's behind
the cowling for the fresh-air intake for the heater - don't have
a clue where for a 3er.. remove the nut (and washer) holding the
linkage to the motor, try to prevent it from turning while
you remove it. The arm connecting to it is splinted, but removes
fairly easily (a good tug). Remove nuts/bolts holding motor in
vehicle. Walk it to your workbench.
2. Disassemble: The contact you want are behind the light aluminum
plate that covers the big gear (this will be fairly obvious).. on
mine, the plate was held on with mashed over aluminum studs. Right
next to these studs were holes through the plate and corresponding
holes into the housing.. sorta looked like these could be tapped to
take a few screws for reassembly (CLUE!).
3. Repair it: Drill off the mashed over aluminum heads of the studs (1/4" 
bit works fine). The cover should remove easily. You'll find lots of nice 
brownish grease. Clean the contacts (attached to the cover) and the face of 
the gear where the metal segment is). Regrease lightly with a white lithium 
grease (at least that's what I used)..very lightly!
While apart - tap the holes in the aluminum housing - I *think* I
used 4-40 American (looked about right, and I had the tap and some
short 4-40 screws, but it might have been 2-56). Try to keep tap
filings out of the housing (grease on the tap helps a lot).
4. Reassemble: Put the cover back like you found it and screw it back
together. Reinstall motor in car. Align the motor by starting it once
WITHOUT the wiper arm attached and letting it go to the park position. Once 
it's aligned, refasten the wiper arm in the correct parked position (try NOT 
to turn the motor while tightening the nut holding the arm).
5. Pat yourself on the back - for $.02 of grease you've saved about $300.
The entire process on mine took me less than 1 hour - and my motor was
not too easy to get at.
6. Send me EMAIL thanking me.
Of course as usual, you may be a klutz with 6 thumbs.. you might have
the hood fall on your head and kill you.. the waste product from an
airline toilet could fall on you and drown you. Whatever.. it's your
fault - not mine. Your mileage may vary.
Best.. and let us know how it works out..
Don Eilenberger
 331 Newman Springs Rd.
 Red Bank, NJ 07701
 Voice: 908-758-3167
 FAX: 908-758-3166
 EMAIL: dje@mail.bellcore.com
Taken from http://cbsgi1.bu.edu/bmw/bmw_new.html
Wiper Info