Cruise Seems Lean

GM used manifold vac adv [ MVA ] & only changed to the useless PVA because of higher HC emissions with MVA. I really wonder how much difference it made to overall emissions because removing MVA [ more timing at idle ] reqd more throttle opening...& more fuel....because it made the engine inefficient.
One of the few things Mother got wrong was failing to use MVA.
Although MVA was there in the background, even on Mopars, during the 70s. Engines had a temp switch so that once the engine started to run too hot, PVA was switched to MVA. MVA increased engine speed [ engine making more HP ], which increased w/pump & fan speed & cooled the engine.