Taurus Misfire Codes

have a 2002 Ford Taurus that threw a P0304 and a P0316 code. Cylinder 4 misfire and misfire detected in first 1000 RPMs. Changed the plugs and wires. Plugs seemed fine, no oil or carbon buildup at all. During drive, the Check Engine light came on again. The codes this time were P302 and P316. Still had the misfire at the first 1000 RPMs but a misfire in a different cylinder. The light is intermittent. Sometimes it comes on and blinks causing rough idling and sometimes it stays on and seems fine. Sometimes it goes off completely. Could it be a bad injector or possibly EGR valve? Thanks in advance. Prior to these codes the thermostat went bad and stuck, causing overheating and a ruptured coolant recovery tank. Replaced and seemed fine for a couple of days. Now the misfire codes. Thought it could be a coil pack or even the intake manifold. Any help would be beneficial.

Water/Coolant in the engine,sparkplugs,plugs.
Faulty O2 Sensor
Faulty PCM
Faulty or Broken Distributor.

Is there a way to check the O2 sensor?

First off I usually recommend potentially serious engine problems being checked by a mechanic with the proper tools.

Omitec makes an O2 Sensor Test kit but it is somewhat expensive. There is an alternative method used to test an O2 sensor using a propane torch and a multimeter but I have heard it can damage a good O2 sensor.
A mechanic would be your best bet but a diagnositc might cost as much as a new set of O2 Sensor, which in itself is not cheap.

My biggest fear is that I blew a head gasket or warped the head due to the original overheating problem from a thermostat. There is no water, oil, etc... on the spark plugs but I can not help think the two problems were related because the misfire did not happen until I fixed the overheating problem. I drove it for probably 15 miles with the Check Engine light on because the gauge never showed it to be anywhere close to hot. The gauge showed it just under the middle which was where it usually stayed after warmup. The initial code showed cylinder 4 misfired. changed the front half of the engines plugs, wires but not the back because they are hard to get to. Now cylinder 2 misfires which still has the old wires. I am puzzled and am almost to the point of taking it to the ford dealer.

I should have asked this earlier. OHV or OHC? And Mileage?

You might just be due for a new set of plugs and spark plugs?

Thanks for the info guys. I finally found the problem. It seems that #2 cylinder spark plug was bad. The ceramic piece inside the plug was completely gone. Replaced it and the wires and she runs like a top. Thanks again.

You might want to consider changing out all of them if it is the OHV it can become pissy if the spark plugs aren't change in unison and if the service date is close changing them on the OHC.

I have a question. I THOUGHT I had the car fixed. Worked for almost 2 days with no engine light. Light came on this morning. Have not read the codes yet. If I blew a head gasket is it possible that coolant in the cylinder chamber caused the spark plug to disintegrate if it was really hot. I think maybe the new plug temporarily fixed the problem. However, I would think that if a head gasket was blown that it would overheat pretty fast. This one does not get hot at all.
FYI-The Taurus is a 2002 w/84,000 miles and is the OHV version.