So i have had this explorer for almost a year now. Has just over 100k miles on it. Had to replace a few things but overall very happy with it. its a 2001 Explorer Sport with the 4.0 SOHC engine. Last week while driving i noticed after 30 minutes of driving the car lossed alot of power and the throttle didnt respond as well. Then i really noticed something bad...Car started to stutter/miss-fire if i attempted to accelerate hard or just raise the rpms in any gear past 3.5-4k rpms. It only does this when its been run for 30 minutes on the roads. But if i push the pedal to the floor the throttle seems all out of wack. And soon as the rpms climb up around that number, it starts bucking and miss-firing bad. I took it to a garage but because of the engine they had me go to a Ford Dealer. $650 later they said it was clogged PCV valve lines and replaced all the lines, the valve, new intake gaskets, and cleaned any gunk out of the intake manifold and TB. I finally got to test it three days later and same problem if not worse. Just put plugs in, cheap autolites but new, the wires are a cheap pep boys brand about 25k miles old and still same problem. Tried putting a new coil pack in but same problem. Im lost and in need of help. Ive heard the mass air flow sensor being dirty could cause this, i installed a warm air intake months ago so im gonna try to clean it tomorrow. Any other ideas??????