Doing this type of thing in damp weather is usually an indication of an ignition system problem. You don't say how many miles on the car and what has been done to it. If you haven't done so recently, I would start by replacing the spark plugs, distributor cap, distributor rotor and spark plug wires. The plugs should be replaced every 60,000 miles if you use the recommended platinum plugs; 30,000 miles for non-platinum plugs. If that doesn't help, I would run checks on the coil and the coolant temperature sensor (Toyota calls that an ECT sensor.) To do these checks you will need a DVM and the specs from the sticky at the top of this forum.
Mike