Been trying to get ideas on what people think this issue could be. I'm lost at this point. When cold. Car idles, shifts from park smooth, and runs well. When warm. Idles rough, engine shaking, shifts from park hard, performance loss. I don't understand what would cause that difference other than the choke. Which seems to be adjusted and working properly. Anyone have ideas other than that? No amount of timing or idle / fuel mixture adjustment while car is warm fixes the issue. Changing from manifold to ported vacuum changes nothing either. I sprayed around for more vacuum. Found nothing. Reseated the intake manifold and carburetor. Made sure the throttle blades were closed properly in carburetor. Replaced hosing. Readjusted mixture and idle. Switched from manifold to ported vacuum and retimed. Issue still persists ONLY WHEN WARM. I read on a classic Mustang forum somewhere that someone was having a similar issue and replaced their PCV valve and that fixed it. I ordered a new one, so I'll test that when I can. But otherwise. Does anybody have any ideas? I'm frustrated.