My vans seems to run just a bit off after cruising for an extended period of time, say 3 or more hours. Misfire is actually too severe a term; it just doesn't seem quite as smooth as it is in the morning. I definitely will notice how well the engine runs the next morning on a trip for example. Note, my coolant temp is fine.

Van has new NGK plugs, OEM wires, new Bosch rebuilt dizzy and a new Bosch coil, as well as recent Bosch cap and rotor, so it seems that the ignition system should be A-OK. Timing set per TenCent's method. I checked for vacuum leaks, spraying brake cleaner (although engine was cold) and did not find any - but I am still think that is a possibility.

The blue coolant temp sensor was replaced 6 years and perhaps 10-15,000 miles ago.

Any thoughts on what to check?\

John