My ford explorer 1994 xlt 4.0 engine, it feels like it is miss firing at times and then corrects itselft, l'v change the wires and plugs, and somebody told me it might be a egr valve or oxygen sensor. I'm not sure if this 4.0 has an egr? Would you give me some advice on trouble shooting this problem?
If you've eliminated the plugs/wires as the cause, then continue by checking the coils. Because a faulty coil pack could be your problem.
You do this with a spark checker to see if all plugs are firing.
A lean misfire would mean one/more of your fuel injectors are clogged or not firing.
You can listen to each injector with an automotive stethoscope. You'll clearly hear the ticking sound of the injectors firing. If not, replace that one. Next would be a flow test, which of course is more involved.
Finally, your egr valve is located on the drivers side of the engine, in the middle towards the top. It's round and has a vacuum line and exhaust tube connected to it.
I doubt this is your problem, but you can check it anyway.