4.0L Problem

[fes007]

I have a 96 4.0 liter OBDII ranger. For some reason it has been running really rough at idle to the point where it sometimes stalls out and dies. It idles at times around 400 to 500 rpm but very rough. The engine has a tendency to lose power after about ten minutes of driving especially when it is cold. I can start the engine back up and the problem stops. I have replaced the MAF, fuel pump, fuel filter and the air filter. I don't have a scanner and it is not throwing any codes. Since I have put the new air filter in it seems to be running rougher. It is almost like it has a miss to it. Sometimes the idle will surge at a stop hovering from less than 500 to a 1000 rpm. The fuel pressure is fine but this is really starting to stump me. Someone was saying it might be the Throttle positioning sensor but I think it might be the Idle Air Control Valve. Any help would be appreciated.

 

[michowski]

Have you checked your timing recently?

 

[fes007]

It isn't the timing because whatever it is it resets itself when i turn the engine off and restart it.