Just bought this 1997 F150 with a 4.6. I am stumped. Here are the symptoms 1st. Hard to start when it does start not much throttle response when idling when I put it in Gear it loses almost all response and nearly moves. Managed to drive it home last week but it was a slow go at 1st seems to have a miss and it backfires through the throttle body. Managed to get it up to speed by shifting gears and taking overdrive off. Now what I have done changed plugs checked firing order changed TPS and coils changed injectors and fuel filter. Any ideas.....?

 

Get your cats checked, they could be plugged. Borrow or rent a fuel pressure gauge and see what your fuel pressure is.

Check for OBD2 codes.

Why did you change the plugs and coils without also changing the plug wires? Did you do a compression test when you had the plugs out?

 

You didn't say how many miles on that truck but I'd be more betting on a slipped timing chain.

 

Just a suggestion, I have a '94 T'bird with the 4.6. A few years ago it was doing the same thing. Turned out to be the MAF sensor. Did you try to clean it prior to the problem? A friend of mine had a cougar with the 4.6 in it and he tried to clean his MAF and screwed it up. Just a thought.....