2006 Dodge Stratus engine idle

I've had the fuel injector cleaned, cam, crank and fuel pump sensors replaced and it still loses idle from 750 rpms to below 500 (stearing wheel vibrates excessivley) then most of the time it catches itself and revs above 1000 rpms and settles back at 750. It happens while in drive too, even while pressing on the accelerator. Rpms drop and a few seconds later it'll take off like a bat outta hell. No check engine light and usually happens after a 10-15 minute drive.
What's the next step? My mechanic is at a loss.