Idle too high and too low

I have a 1990 pickup, when it first starts it idles very high (not sure exactly what rpm), and then it starts to dip, from high to low from high to low, at inconsistant intervals. If it is driven it will over heat. I also found some water in the oil, it maybe unrelated. Does anyone know whats going on? Plugs and wires are only a few months old!

If you've found water in the oil, the idle is the least of your problems. You need to get the head gasket or gaskets check out and replaced before you ruin your engine!! It always helps to know which engine you have when trying to figure out a problem.

If you've got water in the oil, first check the compression. If good and consistent across the board, the likely culprit is the timing cover. The timing chain gets loose with wear and rubs on the back of the cover, which just happens to double as a water jacket going into the water pump. A new cover is only about 75 bucks and timing set is approx 50 bucks. Not a hard fix!