1999 Ford Taurus 3.0L V6 24V DOHC Duratec Engine Engine was misfiring, plugs replaced, KAM erased, Idles Slow and Rough. OBDII says misfire ocurring on cyl 4 & 5. Codes P0300, P0304 and P0305

Check coil pack they can go bad even when not many miles. Also check plugs. Check the code see if it is a misfire. Vulcan or Duratec engine?

Almost sounds like maybe a motor mount issue.

Need to get a can of gumout and with it idling spray around the top of the upper plenum to see if you have a vacuum leak if you have a leak it will either idle up slightly or kill the engine very very common on the 3.0 Taurus ,little more information would be helpful like how many miles are on the car

What engine? 3.0 OHV or 3.0 DOHC

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

I would start with the intake gaskets. this gaskets are a common problem and would cause the lean condition and the misfiring and also before that even i would put a fuel pressure gauge on it to make sure the correct fuel pressure is being sent to the injectors, i weak pump can also cause this problem, starting witht the intake a smoke machine would be very helpful to pinpoint a gasket leak or using a scan tool and watching your fuel trim values while spraying throtlebody cleaner around the intake and seeing the values and if they change or the engine speed chages, this is where i would start. good luck and have a good day.

have you replaced the plugs and wires, thats usually where the problem lies.

I would suggest replacing the coil pack. Thanks and good luck with your repair.

check transmission fluid.change fuel filter and air filter.try changing up on where you buy gas .because bad gas causes problems.

I dont think it is the PCV but its a good idea to replace the PCV at least once a year either way, and its very cheap, usually $2-$5 at autozone.

Disconnect the battery completely, try turning the key with the battery disconnected. Put the battery back together. The check engine light should be off now..