83 633csi Idle Drops and ICV Stalls the Car When Closed

[jimmeek]

I'm helping my son with his 633. He purchased it about a year ago ago and it was running great until the clutch pedal went away. We just replaced the slave and master clutch cylinders and I also removed the cluster since we weren't getting the tach, speedometer, and temp reading. I just replaced the battery with the new board. When we started it back up we were able get the temperature but I still need to work on the tach and speedometer. I can trace the electrical diagram and figure it out so right now I'm not worried about that.

Upon start up we started getting a hunting idle after the initial cold injection of say 30 seconds. From what I have read this is usually the ICV so I pulled it to clean it and it is clear. I blew it out with brake cleaner just to be certain and I checked it with a 9 V battery. It closes completely when energized. I put it back in the car and nothing changed. I checked all of the hoses and found one crack which I sealed up with electrical tape until the new hose gets here. Now this is the weird part. When I close the ICV with the 9 V battery the car immediately stalls. I assume since this is a two wire unit that it is just on or off? Is this correct or does it modulate? If it modulates I need to check the signal wires from the "Solid State Relay." Where is this located as I don't see it anywhere in the electrical drawings like all of the other relays and connectors?

Any help would be really appreciated.

[shogun]

moved to E24 forum

[DesktopDave]

I'm not sure about the ICV, I believe it's spring-loaded open. I always guessed that the control unit sent a PWM signal to close the shutter against spring tension. Later Motronic models did use a three-wire ICV.

There is a small dedicated idle computer on the early models. BMW does describe it as a solid-state relay, but it isn't. Looks like a complete digital control unit with a lot of terminals. I'll attach a few pics of one I pulled recently.
IMG_20171217_220101.jpg

[DesktopDave]

That little computer should be mounted above the glovebox, near the DME/ECU. They vary in color too. Some are green, some black, there are probably other versions too. If you decide to replace it, be aware that the part numbers must match the DME. They're part of a set, along with the AFM.

There's a really good Motronic step-by-step troubleshooting guide here too:
http://hiperformancestore.com/Motronic.htm
Ignore all the M5 and Alfa stuff if you check out that link above. It's helpful but a little confusing. I printed out a copy, removed all the stuff that didn't apply to my car, and left it in the glovebox. Since he's been so kind to write, update and host that troubleshooting guide, I'd like to give him a free plug: I'd definitely recommend his silicone rubber hose kits. These motors are so picky about vac leaks that new hoses can solve a lot of problems. They're clearly not OEM/stock but don't look bad if you order a set in black.

You should have Motronic 1.0 Basic on your 633, with the 2-wire ICV. It's pretty similar to a lot of other engines around that time period, I owned a 325e with pretty much the exact same system. Some earlier E24 models, especially Euros, have something called an AAC that was thermostatically controlled, and the later models has a 3-wire ICV.

[DesktopDave]

Gauge clusters are fun. Most of the troubles I've had with them are the SI board batteries. I've also had a few with damaged traces on the mainboard, loose mounting nuts and damaged or mismatched individual gauges. That cluster shares a lot of parts with the E23, E28 & E30 so spares aren't impossible.

Tach gets a signal from the DME, look for a small three-pin connector near the main DME plug. It's called C102.

You should have the later e28-style gauge cluster with a digital speedometer, that signal is generated at the differential. I've seen a few of those sender plugs corroded inside the wiring boot at the rear diff cover, cleaning them up solved an intermittent speedo problem on my 318i. I also once had a sender that was cracked internally...those rusty little 10mm bolts were the worst part of the job!