AutoPEEP is gas still in the lung when the next breath starts. The T1 can estimate it. Your eye on the flow waveform is faster.
Why transport makes it worse
People raise rate to 'fix' etCO2, shorten Te, then wonder why MAP fell. The high intrathoracic pressure is a Valsalva.
Math you can do
Time constant τ ≈ Rinsp × Cstat. You need about 3τ to empty 95%. If τ is 1.2 s, Te needs to be ~3.5 s. That is a rate of 12 with a short Ti — not 20.
The emergency move
Disconnect, long slow exhale, press on the chest if you must, reconnect at a lower rate. Then bronchodilate.