Hey guys, brand new member here! I just bought a 99 E-150 4.2L, and it just started having this problem......It idles pretty good, but when you hit the gas, it just kind of cuts off all acceleration, and feels like you just came off the gas with your foot. But, it happens only after you are on the gas for about a second. So weirdly, I can drive it no problem if i just hit the gas for only exactly one second, then come off for 1, then back on gas for 1, then off again 1 second, and so on. And on and on, all the way up to easily 50 mph with no problem, but as soon as you forget to come off the gas, it just does it for you! Then, if you wait a second, you can hit the gas for on 1/ off 1 again....
So, it seems to happen in all gears, because it doesn't matter if im on the highway, or taking off from a stop. So, I'm not sure what this could be. It seems rather like a minor problem, but the owner said he was gonna junk it because he thought it was the tranny, but I'm pretty sure the tranny and motor are fine. It idles fine, and revs fine and strong, with 150k, and the owner was a friend so i know good general upkeep on her.
Again, it is hard to explain, but the best way i can describe it, is if you just give it some gas, a lot or a little, it accelerates fine for about a second, maybe 2, and then does what feels just like coming abrubtly off of the gas, jerking you a bit forward. And, the only way im driving it is by doing that annoying on for 1 off for 1 second pattern, and thats getting old fast. And, it never actually stalls out. It just cuts off gas, and lets it pick up again a second or two later......really weird. So, im hoping I can fix this and its something stupid, instead of having to junk her.
So, any ideas on what this could possibly be? Everything else seems to be running fine. I know he just changed the belt too, so I don't know. It seems almost like a sensor maybe? Any advice or ideas would be greatly appreciated. I have been working on cars for a long time, but this is my first truck, well van.... Thanks in advance for any help, and thanks for letting me into your forum. This place seems like it will teach me alot, and i am hoping to. So thanks.

Dave

oh, and the Service enging soon light came on the same time the truck started doing this weird thing(a few weeks ago and then got parked but now im trying to drive it). Im trying to borrow a universal diagnostic thingy from my friend, so yea.
Oh man, i hope its not the fuel pump.....