Need some advice please people.

Drove my Saphire (k reg) down from Edinburgh to Portsmouth last week with no problems. Needed a wash, so I gave it a jetwash to get all the crap off.

Took it for a spin on monday - It seems to be 'hesitating' when the revs stay constant in any gear, even at 70mph in fifth. When you put the foot down there is a little pause then it goes as normal as the revs rise. Idle seems to be fine. Its hard to explain but it just seems to lurching, but only slightly and you can feel it through the pedal.

I gave the coil connections and the plugs at the dis cap a good wd 40 spray and cleaned then up. The problem is still there although not as a bad as it was at first.

The car was serviced 1500 miles ago with new plugs, dis cap and rotar arm.

Is this due to the jet wash or is something else causing this?
Any advice would be much appreciated.

Leigh