Hi. I recently purchased an 06 Civic EX with 144,000 miles on it. Vert intermittently, and most often under load, it will misfire or stutter, but only at a stop. We have replaced plugs with new NGKs. It has a new MAF and new air filter. It seems to idle rough at a cold start, but once in gear, the idle quiets. One time, it stuttered at a stop, until a flashing CEL came on. I turned the key off and restarted and drove directly to the dealership without incident. The technician stated there was no code stored. Dealership tried to sell several "treatments" ( fuel treatment for 249.00 and a 249.00 valve job), although could not confirm that those things would solve the problem.They did perform a PCU update at that time. I have driven the car another 1000 miles and it seems the problem disappears as long as I dont use the air conditioning or defrost. Can anyone advise?