<E28> Idle Control Valve Saga

["Chip Baines" <ebaines@xxxxxxxxxxxxxxxx>]

When the idle control valve on my '86 528e quit working, the result was the
engine would continually surge from about 800 RPM up to 2,500 RPM and then
back to 800 RPM, in about 4 second long cycles.

The problem started when I decided to clean the engine compartmnt.  First I
covered the ignition coil and fuse box with plastic baggies, then I sprayed
the dirtiest areas of the engine with P21S Total Auto Wash, and then I
hosed the whole thing down.  The engine is much cleaner now than it was --
that's the good news.  The bad news was that when I started the car with
the engine still wet, I suddenly had the surging problem.

I learned from researching the Bentley manual, various repair FAQs on the
web, and other digest postings, that this problem is usually due to either
a faulty idle control valve or the idle control unit.  Both items are
pretty expensive to replace, so it would certainly be wise to know which
one is busted.  My guess at the time was that I must gave shorted something
out when I tried to start the car while it was still wet.  Following the
procedure outlined in the Bentley manual, I removed the idle control valve
from the car, and then applied 12 volts to the two electrical terminals. 
That's supposed to cause the plunger inside the unit to move.  Well, what I
saw happening was only just a slight "twitching" of the plunger.  It
obviously wasn't sealing properly.  However, it seemed to want to work, and
with an ammeter I found that it was drawing about 1/2 amp (as it should). 
A couple of shots of WD40 to clean it right up, and it started working much
better -- now applying 12 volts causes the plunger to jump like it's
supposed to.  I thought I had the problem licked, but when I put the valve
back into the car and started her up, I still got the surging.  So, I guess
that wasn't it after all.  Back to the book.  Next step is to check for
proper output from the idle control unit by checking the current with the
ammeter at the electrical connection to the valve with the engine running. 
It's supposed to be 1/2 amp, but I measured 0 current.   I also found that
when I started the car, and then jumped 12 volts across the valve's
terminals, the engine would quit (as it should). So the valve was
definitely working, but was not getting any control signal.  I was about to
check the input and output of the idle control unit itself, but it's a pain
to get to (it's mounted above the ECU above the glove compartment).  So I
thought before doing that I should inspect the wiring a little closer. 
Looking at the electrical connector at the control valve, it seemed a bit
flimsy. Hmm, let's see, I can open the connector using these two plastic
tabs.  Ah hah!  The wires have broken inside the connector!  Simple job,
just re-solder the wires, tape them up to provide a little strain relief,
plug it back together.  Now it works good as new.  No need for any
expensive new parts at all.  All is well.

Lessons learned: (1) Be extra careful when you spray water around the
engine.  (2) Idle Control Valves tend to get gunked up over time -- a quick
spray of WD40 or carb cleaner can improve its operation.  (3) Electrical
connectors can break *very* easily, especially on 12 year old cars.

- -Chip Baines
 BMW CCA

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