It did turn out to be the air flow sensor. There was a spot worn through the carbon strip where the wiper made contact with the potentiometer. I'll order one and replace next week. I was able to position the pot so that the worn through spot was not in the path of the wiper, so that did get rid of the surge, but as I suspected, it idles a bit too fast.

I may try one of the $50 after market products and see how it works. Has anyone had any experience with them? If so, I'd like to know how it worked.

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92 300E - 116K miles - Sold
77 Euro 350SL - 67k miles
94 Explorer 147k miles
2009 Hyundai Genesis - 65k miles