If there is enough carbon buildup on the valve they talk about, it could keep the valve from closing all the way letting air back into the engine. You could temporarily remove the SAP, block off the hole in the head with a block off plate and see if your problem goes away. You'll get a check engine light but if you put the SAP back in after the test and clear the codes you should be good.
When was the last time you changed your spark plugs? This can cause rough starts too...
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