Car misfiring after power hosing engine

I almost never use my car. I has been good since I bought it, 2005. I washed the engine [I always do that twice a year] with power hose. When I started the car it began jerking. Thought it was just the recent wash. Waited two days, then I drove it again but was misfiring badly took a lot of gas to drive 8 miles. Mechanic with computer told me that cylinder 3 was misfiring. Light engine went off. Today it is almost normal but still misfires a bit, in particular when idle or reverse.
Want to hear something funny? I have noticed that when I start the car and turn it off , at least three times, at the fourth time the jerking is less. Do cars begin at different cylinders in every start? Or is it just my imagination that car jerk less when I start/turn off at least three times in a row. Anyways; any advise guys? Thanks a lot. JC