Had a problem with my 2.4, 2004, manual, saloon, exec accord. Rough idle and the engine would stall at standstill. Also, the management light was on, reporting the cat was not performing to the accepted standard. Replaced the cat and the pre cat lambda sensor (£400) but it's still doing it. Also replaced the spark plugs with NGK iridium ones, put a K&N air filter in and it's still doing the same. I've read that the problem may be a vacuum leak and I've noticed the temperature gauge is running slightly low (if 1 is cold and 10 is hot, 5 should be normal but mine's running at about 3). Are the temperature gauge reading and the low idle related due to a vacuum leak? Any advice would be much appreciated. I'm going to try and spray some carb cleaner around the engine (carefully as it's flammable) to see if anything obvious comes up but has anyone come across this problem. Engine runs fine when moving, it only runs rough when idling. For a 2.4 engine, I would expect a bit more power but I've never driven another accord to compare mine to. It's a lovely smooth ride but just doesn't have the balls I'd expect from a 2.4 engine. Feels more like a 1.8 at the moment... The throttle body and the butterfly valve has also been checked and cleaned.