1982 - 84 533 How do you know when the ICU has failed. What are the Symptoms?

[Kenneth1948]

1982 - 84 533 How do you know when the ICU (Idle Control Unit behind the glove compartment) has failed. What are the Symptoms?
Thanks, John KennethIdle Control Unit.JPG

[royemello]

wont run worth a sh%t - if at all - ck the plug ends - they get corroded & bent - also read bentley book about it - some must have 1 leed removed issues w/ a/c & idle control. but usually its just the contacts. unless u got temp sensor, injector / wiring issues.
but the 02 sensor & ICV & dme can screw up - ck everything at the DME (bentley dme motronic tests) 1st ? - & at our age of cars always have a spare

[Kenneth1948]

Thanks Royemello, your first comment accurately describes my problem which I have been battling for many months. Starts and runs extremely rough and way too rich at idle.
I have eliminated common causes. 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. They seem to be prone to failure and a new OEM part is very expensive.
Summary:
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)

• Fuel pressure is normal.
• Disconnected fuel to cold start injector. No change.
• Changed out idle control valve.

(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.
• Checked TPS. Good according to Bentley
• Removed exhaust system. Actually runs better at 2000 rpm + but no different at idle.

[royemello]

if u do all ck's (bentley @ dme) - all with in specs - swap out ICM - - but also - ck fuel pressure @ rail (before & after regulator) - if pressure control regulator is blocked - will = too much pressure in all injectors - make sure return line is good (not blocked) too. when return line is disconnected - ck'ing regulator - blow air thru it - (not too hi pressure) remove gas cap or u can blow off tank evap lines - ck those too (old age) make sure evap canister is not blocked. & (if u have it) ck e vap accumulator (gray box) & lines in trunk.
?? too much fuel in sys - ICM , DME, 02, pressure reg, (as long as t belt is correct) correct compression.
i always - at 100k ish - change fuel pump (main) & filters (2 maybe) ck line ft to back look for 2 - some do. flush line before attaching to fuel rail- pull fuel rail & replace w/ rebuilt injectors - clean & ck pressure reg, - blow / clean return line. replace all temp sensors, replace 02, & reset ICV (milli amps) per bentley - replace chip in dme w/ e bay $40 chip (performance not race) - E 3 plugs, t belt & ft oil seals -(all of them) belts & ALL hoses & good to go for another 100k

[dlduke]

If you haven't yet figured it out, check the wiring on the fuel pump and check the reference sensor and speed sensor on the bell housing. Could also be a clogged catalytic converter.

[dlduke]

I had an ICU failure on my '87 528. It would rev higher than normal, up and down wildly, and if my memory is correct, even while driving. Cleaning corrosion off of the terminals made a big difference.