Hi--just searched the archives--hoping someone else might have fixed this in the past.
I was getting P1421/P1423 codes and CEL on our '98 328 convertible. Confirmed the secondary air pump had died (it was full of water when i removed it). Also replaced the exh manifold valve and electric valve since everything was orig with 140K. About $460 in parts! Went ahead and replaced most of the vacuum hoses while i was in there.

The only parts i didn't replace were the air pump relay (appears to be working fine on cold start) and a small plastic "non-return" valve on the intake side.

Is it possible the relay could be cutting out, or the non-return valve could still be causing the CEL to come on? After replacing the parts, the car ran great, and no CEL for about 50 miles, then it lit up on the next cold start.

Very frustrating, is there a ground circuit i should check? I plan to replce the relay next.
Thanks! ron_va