Won't Idle, Sometimes

[HOTLNC]

Ok, the brick is starting to do its “will not idle” thing. It’s intermittent also. It used to be all the time, but I replaced the plugs and wires and I thought I fixed it. Sometimes, when it’s first started, if you get off the throttle, it will die instantly. I think I can hear a vacuum leak on the top of the motor, but I haven’t been able to isolate it. Maybe a stuck valve that is dumping vacuum when it shouldn’t. Once it warms up, it idles fine. The other day it did it to the wife and I heard the high-pitched whistle. We parked the car and she took mine. I was running errands and got back to the car about an hour later. It idled fine for me.

It is not throwing any engine codes.

Any suggestions?