Chrysler Voyager V6 1998 - Misfire - katiecuppa

Hi all, I have a Voyager V6 1998. Eversince I bought the car, we have had a misfire. The codes are P0350 and P0351 and at times P0352. We have changed the plugs, leads and coil pack. The misfire was intermittent. It nows seems to be everytime we start from cold, although if we go on a longer journey of 1 hour or more, stop the car and leave it for an hour or so then start and drive after a while it will clear and run as normal. The fuel consumption with the misfire is half of when running normally. The garage have no idea, but one theory that I have is that the ecu (powertrain) and the ecu for the transmission, both sets of wires areopen to water/moisture. Just for info, the pther day in the warm sunshine the car started with the misfire from cold but very quickly cleared.

Sorry for long post, but I am desperate to get it sorted or the car will have to go.

Many thanks.

Katiecuppa.