If your economy (vacuum) gauge is not fully to the left at idle, you still have a vac leak somewhere. An often overlooked source is a small vacuum hose attachment at the intake manifold, rear between engine and firewall. The flexible attachment to that vacuum source lives in a usually oil-rich environment and rot easily. That attachment is hard to see and harder to access. You need tiny hands and a lot of patience.

The method that I know of for hunting down vacuum leaks is a can of starting fluid. If the engine speeds up (or slows down like when it was running super rich), then there's a leak. I found a hose at the back of the manifold between the engine and the firewall. It did not leak. I did find a vacuum leak right at the idle control valve that I'd fixed once before, and I fixed it again. No real change though. At idle, the economy gauge is right at the center. if I rev to 2000RPM in park, it goes most of the way to the left. Sometimes, it sits at 2000RPM, sometimes it decides that what I've set the pedal at isn't what it wants to be at.
I went over the whole engine and used half a can of starting fluid, but couldn't find any more leaks. I adjusted the mixture 2 more turns counterclockwise (for 6 total since I got it back from the shop) but it made no difference to the vacuum gauge. I'll take it out on the road here in a few moments and see if the surge is still fixed. it was intermittent when I first bought the car, so I'd always think I had it fixed and then it would come back.

Thanks again
John