Check engine light on my 99 SH -insufficient egr flow (think it's p0401)keeps coming on-changed the valve, cleaned out the intake ports, it's still throwing the code. Next step Honda recommends is changing the ecu, however don't think that's the problem-the light comes on fairly consistently on trailing throttle (coasting downhill, slowing for toll booths, etc), think it would be more random if the ecu was acting up, also takes a few days to come back, or a few hours at freeway speeds. Car also has cat back (NOT recently installed)-could that be the problem-insufficient exhaust pressure to create enough egr flow, helped along by aging or something else. Any help appreciated, I'm stumped and don't wanna buy a new ecu if that won't fix the problem, spent enough already.