My 5 speed 2.0 jetta (1998) stumbles like a drunkard when its wet out. Now I know that its been covered six million times and it usually needs wires, but it only stutters under load from the stop (idle to 1500 rpm) and when at a lower cruising rpm (1500-2000) and you give it more than 1/4 throttle. These situations only occur when the car is cold and not at operating temperture and its wet outside/raining.
Once it hits normal operating temperature the stuttering dissappears and it drives like normal.
Also, when its being a bitch like this, it doesn't like to start, until its warmed up, then it starts easy.