'95 4.6 liter engine revving??
1995 Ford Thunderbird LX, 4.6 liter V8, a little over 50,000 miles. This is one of those intermittent problems that doesn't seem to have any particular cause. It seems to occur mostly at highway speeds between 55 and 75 mph, but it will also do it at speed as low as 30 mph. While driving at constant speed (usually on the highway) the engine will suddenly rev up. For example, at 70 mph the tach normally reads about 1800 when everything is running ok, but when the engine starts acting up and does it's revving thing, the tach will jump up to about 2800-3000 rpm. Occassionally, it will even jump up over 4000rpm. It usually holds at the increased engine rpm for three or four seconds and then in what seems like two or three steps will gradually drop back to normal. The entire sequence takes about eight to ten seconds. It might do it once, and then not do it again for ten minutes, if at all. Or it might do it several times in a couple of minutes. There is no increase in the forward speed of the car when this happens, but there is a slight lag in forward speed just as the engine starts revving.
On a fifty mile interstate highway trip it might do it ten or twelve times, or it might not do it at all. It does it in warm weather, it does it in cold weather. Sometimes it does it when the cruise control is on, sometimes it doesn't. Anybody have any idea what's going on.