i have a 99 civic, Car drives good for awhile until CEL (code p0505) pops up car feels like it wants to stall in 1st n 2nd gear on low Rpm have to atleast drive 25000rpm for it not to feel like it's going to stall. I reset the Ecu CEL deletes and car runs good the idle issue is only when CEL is On. I Bought a IACV, replaced the manifold /throttle body gasket, checked for any vacuum leaks ( didn't find any leaks). What could it be?

 

You need to adjust the idle speed. See diagram in FAQs sticky.