81K miles on vehicle. Tuneup done approx. a year ago (plugs, wires, intake cleaning, diagnostics). I had this problem before I took it to the shop; that's why I took it in initially. Everything was fine for several months.
what I mean by intermittent is that it may mess up a couple of times in a month then go weeks with no problems. Then it might mess up two or three days in a row. I can't establish a pattern such as right after fueling, weather conditions, etc. I run Berryman B-12 maybe 3 or 4 times a year to try to keep the fuel system clean. It never happens when the engine is cold, only at normal operating temperature.
Before I took it to the garage for this problem, I had the computer codes read at the auto parts store and the fault was "multiple cylinder misfire".
Hope that helps.