Not Another High Idle Thread

[flumph]

Edit: forgot, it's a 1984 325e.

So I've been through the high idle writeup and I thought I had it figured out for a while. Idle was stable at right around 850 or 900 rpm.

Then, when I would start the car (even when warm), it would idle great until I drove around for a few minutes, and then it would settle at 1 or 2 needles below 1000 rpm. It was still stable though, and when I turned the car off for even a few seconds and started it again, it would go back to regular idle.

The other day my gas cap was stuck on. Like "needed a wrench" stuck, but once I filled up and put it back on, it came off normally. Suspect I'm pulling a vacuum on my tank maybe.

I also observed the temp gauge in the cluster flick around for a solid second when I was sitting at a drive through. Thought maybe bubbles in the coolant lines.

Then this started happening...
I didn't touch the throttle at all during this. I don't have any clue. The car also smells of fuel at startup.

The only thing I can think is that maybe the evap canister is saturated with fuel. So I looked down there, and noticed that the check valve between the TB and the canister (present in this diagram as #19) is... well it's nothing. It's missing. My theory is that maybe the canister inlet to the TB is set lower than the inlet to the tank. As the fuel in the canister evaporates, the level drops, and when it gets below the inlet, it opens an air passage to the tank and pulls a vacuum, which at the same time is screwing with my idle like someone is poking the throttle. Maybe?

So what do I do? Should I just disconnect the line from the TB to the canister, plug it, and see what happens? Is there something else that could be causing it?

Before someone cries "vacuum leak":

1. intake manifold gasket, cold start injector housing gasket, throttle body gasket, timing cover gasket, and head gasket are all new (they were all finished)
2. every single vacuum hose is new (silicon vacuum hose kit)
3. intake boot is new

The idle control valve is clean and working. The idle control module is the updated green-case style.

Thoughts?

[flumph]

I figured it out, I think. Sorry if I was a little frustrated in the OP.

I disconnected the evap canister and plugged the hole in the throttle body and it didn't do anything. So that's either doing nothing or working properly (I don't know which).

It turns out my oil fill cap gasket was hardened and cracked from age and heat. Vacuum would build under the timing cover because the gasket was sealing, up to a point where the cracked part flapped in on itself and made a vacuum leak. Replaced it and tightened down my timing cover, and it seems to have gone.

The oxygen sensor also seems to have been contributing to an unstable idle (160,000 miles on a part with a 100,000 mile service life!). As mentioned elsewhere on the board, Etas have the sensor further down the exhaust, and require getting under the car to fix. Switched mine out with one of the Bosch universals that I bought at Autozone, and it's running beautifully now.