I own a 1999 ford explorer v6 4.0 sohc. I got it this summer and it ran great. This winter it idled rough so I hooked it up to a diagnostic test and it said the idle air control valve was bad. I put a new one in and the next morning (cold) it idled did the same way. I then replaced the wires, plugs, and the fuel filter and now it runs even worse. I replaced the wires one by one so its not like I yanked them all off at once. I heard it could be a coil pack or temp sensor or the intake gaskets(plastic). I also was told it could be the little black box attached to the heads with vacuum lines running to the exhaust. I almost went to the store and got a B.F.H!!!!! (BIG FREAKING HAMMER)

 

So does it continue to give you a CEL? Same DTC?

 

I have not hooked it back up to the diagnostic test. I am going today to hook the vehicle up at a garage. I have done this before to every vehicle I have owned and no problems until now. I am not a mechanic but now the basic car repair.