2004 Accord V-6 Coupe m/t with 70k miles. Check Engine light keeps coming on at start-up (slightly rough idle) and then resetting (after several key cycles and some driving), only to come on again the next time I start the car or sit at idle for any period more than 30-40 seconds long.

Car has stored codes for bank-1 uptake sensor stuck on permanent lean condition. However, my mechanic says that both 02 uptake sensors seem to be working properly upon inspection.

Car also stored multiple misfire codes for each and every cylinder (both banks), suggesting that the problem is either bigger than just one bank or involves more than one malfunction. I called my Honda dealer, and they cheerfully offered to replace BOTH O2 intake sensors (if I let them suck on my wallet until its dry) but could not explain the misfire codes anomaly.

Also, and I don't know if this matters, but ever since this car was new, it tends to bog down a little when you get on the throttle hard under load (not at idle). Gradually depressing the throttle produces a fairly linear response, but flooring it makes it hesitate until you lift up a little before giving you full engine power. I always just attributed it to the electric throttle and/or the traction control nannies - you tell me.

I'm really desperate here folks - this check engine thing has been happening on and off for nearly a year now - I've changed the EGR valve, changed fuel suppliers, and pulled plugs (all are clean and unfouled) - and what was, until recently, an intermittent problem, is now becoming a persistent one.

I'm stumped.

Any ideas (and I do mean ANY) that might help would be extremely welcome.

Thanks.

 

I had this problem, and it was the primary o2 sensor (happened twice) and it is not an uncommon occurence with 7th gens unfortunately. Also, its a hefty 125 bucks from the dealer, but it should solve the problem. However, mine didn't misfire, but if set at idle for too long, it would knock hard, and nearly stall out, and stall out sometimes, coming from the a/f being too lean. Maybe since it was running too lean for so long that something was damaged in the fuel system?

Have you had your injectors checked? You say that if you get a fairly linear response if you don't go full throttle, then that would make sense if you're injectors aren't getting fully open, where you depress full throttle to get them to do so.

That's my guess. My bet is on the injectors.

 

Thanks for the reply msedacca. It's not my car, just trying to help someone out.