Who is the EFI guru within 75 miles of Orlando? I went through a living hell with this Exmark two years ago. Some of you may remember that. Anyway nearly the same problem is back. It started stumbling a few weeks ago. I blamed it on the o2 Sensor that had a minor cut in it's lead. Finally a week ago it was dead. I took the o2 out and it looked like it had felt growing on it. Same with the spark plugs. I got a new o2 sensor and plugs and it ran pretty good for 20 minutes of so. Now it is back to the intermittent stumbling and loading up. It goes for about 30 seconds or so then loads up. Apparently the o2 sensor was not the problem, it was merely a result of whatever else is going on.