Check all the basics, plug wires, codes(check engine light), Vacuum tubing, etc...could be alot of things, but probably not in the O2 system...also, your local parts store should be able to loan a tester for the Check engine codes...:)
No gas in the engine
Mine did that I replaced the abs sensor.
Take off shudder is most commonly caused by one of three things. Broken motor mounts, a broken transmission mount, or bad u joints will all cause the shudder.
ive had a couple of work trucks over the years which started to shudder. both needed auto transmission work.
I just had the same problem with my 1994 Ford Thunderbird, to make a long story short, the torque converter was bad. Mine had gotten really bad and started making a rattling noise. At any rate after I finished the change, it runs like a champ. No more shudder.
I had this problem and tweaked the throttle and replaced the catalytic converter - fixed.
Warped rotors
I also have a 2000 Venture same problem. Solution was tire balance weights fell off. They were replaced and problem resolved but....the tires were worn irregularly on the inside and I had them replaced.
I had this problem on my 940. It started as a slight shudder when I braked, and then there was an intermittent clunk. Then, without any warning, both of the front brakes fell off (Completely. They were dangling by their cables!). It turns out that the bolts holding the brake system on had vibrated themselves out. Try tightening the bolts and see if that helps.
Had the same problem on my '00 4.7 liter. Turns out it was the throttle position sensor. Sensor was replaced at dealer problem disappeared.
Could be lots of causes, but most likely either rear differential issue or torque converter shudder in automatic transmission, though Ford is not nearly as common to have transmission shudder as a Chrysler is. Mine was the rear differential. (98, 5.4l). Mine was most pronounced when accelerating around a corner. Transmission shudder would most likely show up on acceleration at any time.
The year, make , model and engine info would be helpful in answering your question.