I bought a 92 Civic VX.It runs great as long as you are on the gas but when you try to run at a steady speed it begins to run rough.It does not do this until engine warms up to temp.Its failing emission test for hydrocarbons.No codes are showing.Ignition parts are all new timing perfect.Could this be a sensor even though theres no code?I dont think this car will ever pass the test with this type of miss and I cant afford engine swap right now.If anyone has any ideas please let me know.