P0505 Honda - 2002 with a V6

Question

Problem started with service engine light P0401 code EGR valve. removed intake manifold cleaned air way. reassembled and got same code plus P0505 IACV. Replaced the ERG valve but still have the P0505. have checked vacuum lines and can't find a leak. but car idles at 1200rpms occasionally surges between 1200 and 1600 rpms. also the TCS light comes on after driving a short distance

Answer 1

P0401 EGR insufficient flow

P0505 Idle control system malfunction

You have a vacuum leak, when the engine occasionally surges at a high RPM this is a vacuum leak, This type of engine is a speed density, There is a vacuum leak , this vacuum leak is not going to come from a vacuum line but what ever manifold you removed, the leak is  from its gasket.