wont start when cold

i did both head gaskets on my 98 venture back in aug,been running perfect till now.turns over good but when its not warmed up i haft to put my foot on the gas for a split sec to keep it idling,then the idle catches and all is well,starts right up the rest of the day.walk out to start in the morning and same thing.this has been going on for a week straight.anyone have a clue? codes checked out good.any help on were to start would be great.