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I have a 86 525e. It has the l-shape 2 wire ICV.

I was replacing a hose to the ICV and wanted to give it a quick clean. I found a zip tie waged in there. I don’t know how to describe it, kind of wrapped around the closing part?

Any idea why somebody would to that?? I removed it for now (maybe not a smart idea?!). Car idled fine before, I checked the ICV with a battery and it „clicks“ fine.

I hope the car still idles fine when it’s put together again

I hope you took a pic ! I once found machining plug that goes in the cam chain timing cover (small freeze plug) in the oil pan. Nothing surprises me any longer..

My guess would be it wasn't working right and someone used it as a spacer to try to get it not to stall at idle. But that's no more than a guess.

Remove it and you may find out why it was there

So it turns out the zip tie was there most likely to hide or „solve“ and idling issue. The engine is back together and I ran the car without the zip tie in the ICV.

As soon as I push the clutch the the idle starts surging up and down in a very consistent, rhythmic way.

I just swapped out a lot of the vacuum hoses so I am carefully guessing it’s not a vacuum issue. Of course the ICV valve itself is a suspicious candidate. It does operate with voltage applied. The valve closes (?) when the ignition is turned on and hums after. I read about resistance testing the valve but could only find values for the three pin versions, which are 40 and 20 ohms. Mine is the two pin version and measures only 10 ohms. Does anyone know the correct value for the two pin version?

Anything else I can test? I might do a smoke test to rule out any leaks but like I said most things are new. I would like to be as sure as possible that it is the ICV before buying a new one since they are $$$.

Before I purchased my M5 I owned a 528e. I don't know if your car shares the exact same idle circuitry but I recall replacing the idle controller box and it stabilized my idle. You know, that 1x2 inch black box under the dash. Hmm, I think it was under the dash.

Give it a try.

Hi! Thanks. I read about that to but that idle icu is also expensive and hard to get it seems.

I checked for leaks with my fog machine but there don’t seem to be any. I checked the temp sensors and if I understand things correctly this 2 pin one is for the icv. I could not find any resistance specs for it. Mine says measures zero, which seems suspicious?

Did you try disconnecting your 02 sensor while idling, see if it smooths out ? Do this after she's warmed up.

Hi!

Small update: I have found a used ICM and replaced mine. Sadly this does not seem to have fixed the problem. The surging/oscilating idle is still present as soon as the car is fully warmed up. I have tried unplugging the O2 sensor but this also does not change anything.

does putting a zip tie back in there make it run properly?

On US cars and I'm guessing yours, there is a switch/sensor that screws in somewhere around the thermostat. I'm not sure exactly what it does or is for, but it seems to play a role in the idle. It's 2 prong with the terminals really held on by rivets, which loosen up over the years. I've soldered them back on after a good cleanup to restore continuity, they were still attached, but loose. That could be your problem, at least for starters just bridge the terminals for testing. Also, it seems to be more of a problem on M30 cars, but consider the coolant temp sensor for the injection system, not the large brown thermo time switch, but a smaller one with probably a white connector. Those can cause all sorts of running issues if bad.

You might find the videos from this person helpful:

How to Fix BMW E28 533i 633csi 733i Surging Idle Control Valve Module
https://www.youtube.com/watch?v=aDzlJtgZUAg&t=48s

If Im not mistaken, he published 3 videos while hunting down a surging idle problem.

Great post David, those videos were pretty good.
There are 2 distinct idle issues at play though.
Surging/oscillating idle is caused by a bad ICM, this is a well known phenomenon.
Steady high idle is caused by too much air entering the system after the AFM. Whether that's via a vacuum leak, or an idle valve staying too open, the reasons are the same. Too much air after the AFM.
I had hoped the second video would show the cursed ICM being opened and worked on, that would really help people. I've had the Programma units fail also.

Hi everyone!

Yes I watched those videos too, they were of great help. Not sure if he ever fully figured out his problem though. He swapped his ICM for a refurbished one which I could not find available anywhere in Germany or Europe. I did find a used one and swapped it in, however it did not solve the issue for me. Next I tested the two sensors, the 45°C temp switch and the white (or blue) giving certain resistance readings. He latter one, white in my case, seem to be within spec. The 45°C temp switch how ever never closed at any temperature. Since this one is not available anywhere anymore I had to resort to building my own (as is described on a few forums). I used a generic 45°C normally open temp switched and epoxied into the hollowed out old one.

It seems to work as it should and the surging idle is now gone. The idle however is not yet perfect. When the car is really hot, for example after a drive on the highway or similar the idle sometimes is too high (I don't have a rev counter, so I don't know how high exactly). I also suspect from hearing that the idle in general might be slightly too high.

I measured amp draw fron the ICV and I get 500 mA (480 mA is the spec I believe). From my understanding, the adjustment screw should change the amp draw (?). I thought that the previous owner most likely messed with it, so I tried adjusting it myself. However that does not seem to have any influence on the amp draw or idle speed. How sensitive is this adjustment supposed to be?