[UPDATE - Not so fast.] Rough idle no more...for now

UPDATE:

That was short lived. Took the E28 for a quick trip to my parent’s house (about a mile away). Started up great, just a slight stumble at idle in the first 30 seconds, then ran normal. About a 3 minute drive with stop signs and lights, then parked at my parent’s house. [Side note - their driveway is on a slight incline.]

Came back to the BMW after about 10 minutes, get in to start it up and it starts, but stalls within 10 seconds. Try again and it starts, but running really rough, Giving it a little throttle to keep it running and the response is highly variable.

One time I give it some throttle and it responds as expected, but then coming back to idle falls below 500 RPM and either stalls or near stalls. Then give it throttle again and it goes up maybe 500 RPM instead of building RPM’s based on the throttle input.

I nurse it back home with my dad driving behind me with hazards on.

At home I go in to make dinner, then return back to the garage after dinner. It starts on first try and is rough, but not as rough as it was driving home. Thinking maybe I didn’t get the ICV clean enough, I pulled that again and ran carb cleaner through it. Plugged it back in, and it ran a little smoother, but not much.

I also manually pulled the throttle from the engine bay and did my best to observe what was going on. It gradually improved, but I did observe some of the same behavior - RPM’s not building in response to the throttle input.

Twice I also heard a very odd sound - literally sounded like a metal “clink”, or a metal on metal “tap”. I didn’t come up with any reasonable explanation for the noise until my run this morning - it may be the AFM flapper snapping closed. The problem I don’t recall exactly where in the throttle I was when I heard the noise.

I checked the plug wires, thinking maybe a misfire, and tried to let it idle with the ICV unplugged.  It ran ok with the ICV unplugged, but not really better or worse.

After checking connections for a bit, I started it again and it ran fine. Took it for a 5 minute (neighborhood only) shakedown drive, and it operated completely normal.

I’m stumped.

My next step is to look at the AFM, then maybe the distributor and the wires / plugs. Maybe the Throttle Position Sensor also?

I’m all ears for suggestions.

ORIGINAL POST:

The E28 has been idling rough for a while, but not bad enough to cause an issue until today. If you are familiar with M30 BMW motors you know they are not known for idling smooth to begin with.

It has acted up a few different times lately, though with the current environment it doesn’t get driven often, so maybe it has happened each of the last few times I’ve had it out.

But today it was worse, almost stalling every time it was coming back down to idle. See the before video below.

Luckily I knew where to start - the Idle Control Valve. It controls how much air can bypass the throttle, and greatly influences idle speed. It is really easy to access at the back part right on top of the engine.

Took it off, cleaned it liberally with carb cleaner, and put it back on. Total of maybe 10 minutes.

Idle is better than it has been in months. Really glad that was it, it is hot outside and I wasn’t particularly looking forward to tearing into it today.

After video below.