Random misfires only when it warms up... why?

My 4G64 2000 Galant misfires only when it warms up. The first few minutes of driving everything is perfect. Then about 10 minutes into the drive, when the engine temperature is about normal, it begins to misfire and just get worse and worse.

I just replaced all the plugs and wires, but I can't imagine its an ignition issue because everything seems totally fine when it's cold or warming up.

I removed the exhaust before the cat converter thinking the engine might not be able to breathe, and it still misfired.

Any ideas what might be causing it? The temperature specific aspect of it is what's so confusing to me...

My 4G64 2000 Galant misfires only when it warms up. The first few minutes of driving everything is perfect. Then about 10 minutes into the drive, when the engine temperature is about normal, it begins to misfire and just get worse and worse.

I just replaced all the plugs and wires, but I can't imagine its an ignition issue because everything seems totally fine when it's cold or warming up.

I removed the exhaust before the cat converter thinking the engine might not be able to breathe, and it still misfired.

Any ideas what might be causing it? The temperature specific aspect of it is what's so confusing to me...

I have a 2001 Galant that has the same problem. I just done a full tune up and timing belt and my car still does the same thing. I plug my scan tool in and get a misfire code. I can't figure out what the problem is. Have you had any luck finding the problem on yours and if so what was it?