Need help Guys I still having problems with my car studdering idling through 1800rpm

[LeeS97Z28]

I have a 1997 Z28 with 88K miles. It studders sometimes worse when hot.

The BLM are 160 for L and R side of engine. I replaced the air check valves with new AC Delco parts.

The BLM will drop to normal if you cap off the air tubes but my car runs horrible if I cap these off. I have replaced the air check valve with new ones but I still can feel it suck some air into the exhaust but not as much as it was.
I thought it wasn't supposed to do this. I'm confused can you guys check and see if your car does this too.

Why would my car run worse with the air tubes caped than with them not?

Dealer put Stock AC Delce Platium plugs in it about 15K miles ago. Do you think they lie about replacing all the wires and plugs?

Thanks Lee!

[wrd1972]

I had a corroded coil plug wire that did this.
What about the ICM and coil.