2004 Smart car will not accelerate when it is raining

Sometimes, this happens when an engine is just badly in need of service. But most of the time, I've found that the problem is old ignition wiring with lots of dry cracks in the insulation covers. Moisture gets into the insulation and causes electricity to flow out the cracks to an external ground. Put the car somewhere where it's dry and dark. Start the engine, then spray water mist around the engine. You're going to see a light show.