Ok. Been dying to try one of these forums to see if it would help with my problem. Ive got an 05 expedition with 96k on it. Engine sounds smooth as butter other than a little rough idle. The problem is when you go to accelerate and push the throttle past let's just say 10% it will accelerate great for a second and then fall on its ***. If you continue pushing the throttle at the same position it may let go and take of again with no variance in the throttle what so ever??? Weird I know. I've changed all the plugs with no issues at all. Replaces 1 vct selenoid. I'm getting a p420 code and a p0430 code. HEEEEEELLLPP!!!! LOL

 

With those 2 codes, you probably have plugged cats.

 

But my thought was with plugged cats wouldnt the cats have a major increase in temperature? Or maybe they do. According to my scan tool my cats are getting up to about °1700. They do drop back down when I let off the gas. Say at idle (°900 to °1000) or when I'm at a normal operating speed (°1300 to °1500). I don't know what they should be at. Here's another thing. If I watch my scan tool from start up when the vehicle is cold it only takes about 30 seconds for them to get around °1200 that seems really fast to me.

 

That sounds way too high to me - go to a muffler shop and get the backpressure tested.

 

So I pulled the front o2 sensors before the cat and still have the same issue! If the cats were plugged that would relieve any built up back pressure. I've checked the fuel pressure with my scan tool it ranges from 35 psi to 45 psi. No misfire on any cylinders. Oh yea and when the truck is cold it almost run %100 once it warms up is when it starts all the problem