I was thinking the same thing… but I don’t have one… or do I? Read below:
New gasket came in. Swapped it, no change. Bummer. The “old”gasket was sketchy though…
Then I remembered that I had a cheap fog machine in my garage that I bought for smoking intakes… and with the magic of spare fuel line and electrical tape was able to make it fit one of the vacuum lines (in this case, the one that goes the the intake selector on the filter hat). Smoked it… and surprise, there’s a massive rotted vacuum cap on the vacuum manifold that’s gone wide open. I couldn’t see that the end was popped off due the PCV line blocking most of the view. No ****, sherlock. Doh!
After replacing the bad cap, smoke testing showed no more leaks… started it, it idles… barely. Since we’ve ruled out a vacuum leak (plugged the testing line with a vacuum gauge) and my vacuum was quite weak, I decided to try opening up the idle fuel screw… voila. Way, way, way too lean… got it to a happy spot (hard to dial in due to the carb feedback auto-adjusting the mix)… Good vacuum, and good idle with or without A/C and/or being in gear. Ran a KOER test… no codes. Drove it around some (a few stops and hot starts), no trouble. Nothing.