I had somewhat the same problem with my car recently after washing the engine. It was idling rough and acceleration also affected. From past experience I knew that it was an ignition problem from the water. So I checked for water puddles. Externally I didn't find any, but I did find water in 2 of the 3 front spark plug holes. The water was causing a short so it was not firing the fuel correctly. I guess I got over zealous and got too close to the spark plug holes with the pressure washer. I blew the holes out (dried them well) and everything is as it should be.
I have washed many engines (carburated or fuel injected) and only twice i've had starting problems. The important thing to remember is to not be too close and spray directly near the ignition components (carburator, air cleaner, spark plugs wire boots, ignition coils) and electrical connectors. In my case, I have a coil-on-plugs ignition system and I had forced water under the boots covering the spark plug holes filling them with water. I use compressed air to blow-dry the engine well to get rid of excess water and so that I don't have water marks on my hoses. This time I got caught, but nothing I couldn't figure out. I half-ass agree with what Wrentech said above, but I know that you can wash your engine without any problems if done correctly. I've watched how detailers at dealerships get engines clean and shiny. With "sealed" engine systems like fuel injected cars becoming the norm, you can be more at ease in washing an engine. Of course take precautions as I mentioned earlier, it's may not be as "sealed" as you may think.
Thursday, March 14th, 2013 AT 4:32 AM