I've got a 2001 e350 with a 6.8L and 260000 miles. At startup I experience a rough idle for about 30 seconds. More concerning are the high idle speeds that seem to be getting more frequent. I'll be sitting at a light or stop sign & all of a sudden the rpm's start to increase to about 1000 - 1200 rpm. It settles down after a little bit, then will start up again. Any ideas?

 

Been having similar issues lately with my 00 F250 as well. Interested in seeing the recommendations.

 

Mine did that and it was a vacuum leak at the elbow in the PCV line under the throttle body, it was and easy fix.