Prolly intake gaskets...

Or other un metered air entering through cracked/loose vacuum lines etc.

Get out there under the hood with a can of starting fluid (ether) or other VERY flammable spray can (carb cleaner being another), & spray here & there around the engine...like under the intake, by the injectors, etc.

Listen for an increase in idle speed.

, & be careful playing with flammable stuff...