The idle problem I was having got so bad that when I tried to start the brick yesterday it just stalled. I could rev the engine, but once I let off the gas it would shudder and quit. I did a deeper analysis under the hood. I pulled the new flame trap off, checked and tightened it on, checked the air filter, checked the hoses and everything seemed ok. There was one hose that seemed loose though. It was attached to this white and black plastic cylinder:

I’ve been researching and haven’t been able to figure out what this thing does. I pulled and reattached the hose, wrapped it in duct tape and fired up the engine. No stall. I drove all day today and had no idle problems at all. It seems the problem had to do with air intake/vacuum leaks, but I can’t tell if it’s because of this part, or somewhere else along the line. Whatever. Runs strong now.