Is code P0505 thrown?
It seems that you have a vacuum leak or an intake air leak.
You can test for a vacuum leak. The vacuum system represents all of the hoses attached to the intake manifold (IM). Disconnect them one at a time and then block the IM nipple with your finger. Does doing this drop the idle speed to normal for any of the vacuum hoses?
An intake air leak would typically come from either the throttle body (TB) gasket or the IM gasket. Start by checking whether all TB and IM bolts/nuts are torqued to spec. If so, with the engine idling, spray some carburetor cleaner around either gasket and listen for a change in idle speed, which would indicate the location of a leak.