2000 Dodge Caravan During Summer Car Runs Fine Turns Cold Below 32 Degrees

During summer the car runs fine, as it turns cold (below 32 degrees at night) the car starts to cut off when you let off the gas. The deeper into winter you get the worst the car runs, once spring starts the cars starts to run better. There are no error codes, the local dealer says the intake manifold needs to be cleaned if this is true why does in happen only when it is cold (this is the third year in a row this has happened). The car was tuned up last spring (10,000 miles since tune up). HELP!!!