It sounds too much of a coincidence that it started the rough running after it was washed. You've probably done it but I'd go through everything likely to have been affected by the wash first. Is the inside of the distributor clean and dry? No tracking or moisture? Coil tower , leads etc, is it running on all 4? If not it ought to be fairly easy to trace a fault on the cyl that isn't. After that I'd go for fuel, any water in bowls or filter? If none of this then I doubt it's been the washing and go through the rest. Good luck
