the fuel trends with the 99% the 02 sensors are very slow to cycle up and down also get misfiring at mid throttle

 

You have a vacuum leak.

 

Are you getting any O2 codes? Guessing O2 sensor bad is usually a bad guess in these cases even when there is a persistent Lean code. The upstream sensors are designed to switch fast when fuel trims are right around 14.7:1 but the downstream sensors are different and do not switch at all they just slowly drift up and down.

 

Did have a vacuum leak wich helped the fuel trims. No o2 codes thou but does have some slight spiking on downstream o2 senors. Goes lean and misfires at mid throttle. Misfires can be harsh on humid rainy days. Going to do some tests on my catalytic converter and downstream sensors this coming weekend and hopefully rig a homemade smoke machine to look for more vaccum leaks

 

Yeah i should have researched how the trims work more to know that was probably a vacuum leak. I will get a pic of the down stream o2 trends tomorrow been looking online for they way they should look and everybody is sayin almost a straight line which mine is definately not

 

It doesn't have to be a vacuum hose that's leaking, if the crankcase is not sealed, such as a loose oil filler cap or a loose fitting PCV grommet fitting, then high fuel trims will result.

 

Damn this sounds exactly like what my E150's 351 has been suffering from. We worked all day last Saturday on it and found several things gone wrong. First was the pass side header collector had worked loose. We decided to pull the whole Y pipe/cat and ditch the cat and move the downstream O2 sensor upstream of the collector joint I had installed behind the cat back when I built the system several years ago. Once we got it done and put it back under the van, we still had a popping/lean condition at anything above partial throttle. My son said he thought it had a vacuum leak but nothing obvious could be seen. That's when I got out my "CSI" spot light and started hunting and, Wa-la ! I found the leak. The rubber hose coming off the middle of the TB between the bores had come loose from the plastic line leading to a junction block over on the drivers side inside the engine box. This short rubber hose had become dry rotted over the past 22 years so I replaced it with a different newer piece (not the same but it worked) We disconnected the battery to clear the ECM ad let it relearn the fuel map. I drove it around the block several laps and it gradually got running better, not yet perfect but better. When I have more time I'll drive it more and see. I'm also changing all three O2 sensors just incase any got burned out from all this.