Only when it is raining or shortly after a rain my truck spits and spats and even will stall sometimes sitting idle. This has been going on for years. I never got the problem fixed because it actully stops doing it after I get going on the free way. The problem does get worse though if you turn on the blower for AC, fan or the heat. Other wise my truck runs great on a nice clear day.
This is almost always an ignition system problem. You need to carefully inspect (and probably replace) the spark plug & wires and distributor cap or coil pack.
How many miles are on it and when is the last time these items got attention?