I've been trying to figure this one out for days searching the car and forums. It runs perfect except when in drive at idle(at a stop light, drive thru, etc). The idle drops after about 8 seconds of sitting. It feels like it will die but never does. It just goes up and down. It sounds like it's being choked. I've done a full tune(OEM plugs, wires, fuel and air filter, checked all vaccum lines, etc) The CEL doesn't come on but it will pull the code p0420(Catalyst system efficiency below threshold) when its doing the funny idle. I saw that one guy wrote that the P0420 means it's time for a break. I believe it. This keeps me up at night just trying to think through it. I've seen similar posts from years past but have never seen anyone come to a conclusion and solve the problem. I've found no solutions. Please Help.