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View Full Version : 1982 - 84 633 How do you know when the ICU has failed? What are the Symptoms?



Kenneth1948
11-11-2016, 08:45 PM
1982 - 84 633 How do you know when the ICU (Idle Control Unit behind the glove compartment) has failed. What are the Symptoms?
Thanks, John Kenneth586377

88m53453
11-11-2016, 09:53 PM
uncontrolled idle is one, but have to make sure all vaccum leaks are eliminated etc. Bentley book on the e28 is excellent on diagnostics here. Back in the day, I would do the conversion and eliminate the US system and change to the euro version which used a simple idle screw. First one I did was on an 83 533 we had and it performed perfectly for years

bmw6fan
11-11-2016, 10:44 PM
I have a 83 633 that I recently replaced the ICU on. Mine had a high idle around 1400 rpm. I had a few vaccum leaks I eliminated and got it down to around 1200. Some times it would intermittly surge at idle from 1100 to 1500. I replaced the ICU and all is well now.

RSheiman
11-13-2016, 10:16 AM
Many of us have a spare ECU and one reason is the ability to test the one we are running if issues arise. Not sure how rare or costly one is for the 633, for the US 635, they are too cheap to not have a spare.

Kenneth1948
11-13-2016, 06:35 PM
Thanks for all the responses. It makes no noticeable difference to unplug the ICU so it could be the problem or any one of a dozen other things. I have tried a different used ICU but no way to tell if that is any good either. There doesn't seem to be any way to test them and they seem to be prone to failure so a used one is a risk and a new OEM part is very expensive.
Here is a summary of the problem so far:
Car had been running OK for about 12 months.
Driving normally around town then suddenly started running very rough at stop light.
Car will start with clean plugs, idles very rough (see video) and fouls all 6 spark plugs.
https://www.youtube.com/watch?v=SoTyLaXVbHE
(Note strange behavior of vacuum gauge. This is idling, foot off gas pedal)


Eliminated vacuum leaks. (smoke test)
Fuel pressure is normal. (per Bentley)
Disconnected fuel to cold start injector. No change.
Changed out idle control valve. (New - no change whether electrical connector connected or not so still could be a problem there.)
Changed out thermo time switch and temperature sensors* (* ECU sensor new, others not new, all checked per Bentley)
Changed out idle control module behind glove compartment with a used one. (No difference but replacement could be bad too!)
Checked TPS. Good according to Bentley
Removed exhaust system. Actually runs better at 2000 rpm + but no different at idle.

Thanks for all the help, John Kenneth

flyfisherman
11-14-2016, 08:12 AM
Programa charges $80 to repair the ICU.
http://www.programainc.com/categories.aspx?idcategory=4126&cl=1

RSheiman
11-14-2016, 11:22 AM
[QUOTE=flyfisherman;29490294]Programa charges $80 to repair the ICU.


I think prices went up for repair but its around that to test it out which sounds like a decent cost for some piece of mind.

BTW, plugs fouling=perhaps running too rich. You can adjust the AFM ( or MAF or whatever).

Kenneth1948
11-15-2016, 10:52 PM
I have a 83 633 that I recently replaced the ICU on. Mine had a high idle around 1400 rpm. I had a few vaccum leaks I eliminated and got it down to around 1200. Some times it would intermittly surge at idle from 1100 to 1500. I replaced the ICU and all is well now.

My symptoms are quite different, see below, I'm thinking my problem may not be the ICU

Kenneth1948
12-11-2016, 09:57 PM
uncontrolled idle is one, but have to make sure all vaccum leaks are eliminated etc. Bentley book on the e28 is excellent on diagnostics here. Back in the day, I would do the conversion and eliminate the US system and change to the euro version which used a simple idle screw. First one I did was on an 83 533 we had and it performed perfectly for years

I assume you simply replace the ICV with a "manual" one. I suspect this is my problem. No signal getting to the ICV when the TPS tells it to idle.

At least I can isolate the problem this way.

An '83 533 would have the same idle control system as mine so if it worked for you. should work for me.

As you can see, this is not my daily driver. Trying to save it from the junk yard. I just work on it occasionally when I'm not working on other people's cars

88m53453
12-11-2016, 11:39 PM
I'll work on that list for you