My son has a 1992 Ford Explorer XLT with an automatic transmission, and a 1994 engine with 58,000 miles on it and the engine size is a 4.0 V6. After the vehicle gets warmed up, the rpm goes from 2 and then surges to 3 - 3 1/2, and then goes back down. It does this without pushing on the accelerator. Then it will drop back down again and be o.K. For a few minutes and start to surge again. This is at a speed of 55 - 65. We took it in and the mechanic adjusted some kind of bands and serviced the transmission (cost $86), but it is still doing the same thing. My son is 16 years old and this is his first vehicle. I sure hope someone can give us some advice so we can get the problem solved.