01 Taurus rough idle

Hi I hope you guys can help. I have a 2001 Taurus with 184K on it . The car runs fine on the highway but as soon as I get off the highway to do stop and go driving it has a very rough idle when sitting at a light. The engine lite flashes. The code I pulled way a P0304 (Misfire in 4th cylinder) The plugs and wires were changed at about 150K. About the same time I changed the 2 egr switches. Could this be the coil pack? if so how would I go about checking this so not to throw money around guessing. :eek7:

Welcome to the forum!

It could be a lot of things, bad spark plug, bad plug wire, bad coil, bad fuel injector, bad rings, burned valve, etc. Since cylinder #4 is the middle front cylinder I'd suggest you start by removing the spark plug and wire and inspecting for any signs of damage. If nothing obvious, then trade spark plugs with another cylinder and swap the spark plug wire with a different cylinder that has a similar length. Clear the codes and see if you can get the problem to duplicate. Check the diagnostic code and see if it follows the plug, wire, or remains on #4. If it remains on #4 then you get to perform a compression check or dig in to the injector.

-Rod

I'd switch the coil pack to a different cylinder and see what code comes up. If the code indicates a misfire on the new cylinder then that tells you the coil pack is bad.