I was lucky today to have most of the afternoon for working on the E28. Since I’m still a relatively novice wrench, I set me expectations reasonable - need to resolve the annoying stalling issue.
The issue - when the car get warmed up, and the engine was coming back down to idle, with the AC on, RPM’s would drop to 500 or lower and frequently stall.
So, the M30 engine with Motronic ECU is pretty simple by today’s standards, but still has a number of components that give input on idle. I probably read 50 posts on mye28.com related to idle issues.
What I learned - the M30 just plain doesn’t idle smooth. I also learned how the Idle Control Valve works, what the different sensors on the water pump housing were (since it only happened when warm), what the Throttle Position Sensor controls and how to adjust, and what the throttle plate should look like at idle.
With all of that, what I finally determined the issues to be - the throttle body was dirty.
This shows it when I already sprayed some cleaner on it. You can see it wasn’t super dirty, but per the Bentley (and posts I read), you should be able to see just a sliver of light around the edge of the plate at idle. With the built up gunk you definitely could not see any light.
Once I got it clean I could just barely see light around the edge, so I decided not to adjust it further. It is amazing how much such a small amount of extra air getting by makes.
One thing I will say about wrenching in 2019 is - how did people do it before they had a phone to take pictures of everything as they took it apart. I took almost 20 pictures, and looked back at 4 or 5 to make sure i was getting it back together correctly.
Last comment. The internet is amazing, and you can easily find things from back to the early 2000's. Some of the posts I read from that time really surprised me - the internet and our culture was a really different place. I actually felt uncomfortable reading some of those posts.
Overall the internet is better now. I’m sure there are places on the internet that are still like that, and I’m glad Oppo isn’t one of those places.