Little history.... The van had a serious thump when driving from a stand still... usually at a red light. Also, when cruising around a corner, hitting the gas almost always caused a thump.
Shifting from forward/reverse also causes thumps.
I had attributed this to multiple broken motor mounts...and was about to replace these.
Before doing this I decided to replace the O2 sensor on the cat...I was showing a ODBII code... no point in replacing the mounts if I fail inspection!
After replacing the O2 sensor... the thump is gone?!!! The van now shifts nicely! I still feel a thump going from Forward/reverse...this is due to the mounts.... But the annoying thump while driving is gone.
I guess the control loop that uses the O2 sensor was completely out of wack...and was giving the engine way too much fuel when accelerating?
For those of you experiencing this... think about your O2 sensor!