2006 Honda Element P0300, P0302, Struggling to idle

I have a 2006 Honda Element with 235,000 miles that is struggling to idle once warmed up. I got fault code P0300, P0302 and P2646 for misfires and vtec oil pressure switch low circuit so I replaced the spark plugs, coils and vtec solenoid and the Element still struggles to hold an idle below 1000 rpm. Took it to a shop and they replaced the alternator and the problem still exists. Once I get the Element to above 1000 rpm it runs better. Any suggestions?