Would it damage your car if you power washed the under side of the engine?

Sounds like you got something wet & it needed to dry out before starting. You probably didn’t damage the car…just gave it a temporary shock. I don’t know that I’d try that on the newer computerized cars as it could easily blow the Mother Board & cost $2,000–5,000 to repair. You might want to read more here.

You probably got some water or water vapor/steam in the distributor cap. Should be OK after it dries out. You may have to take the cap off for it to dry completely. No other problems or damage should result from washing the underside of car/engine.

^Yeah . D cap, or air intake…