I recently bought a 98 xj and it preforms well when driving but while it’s not driving and just in idle the oil pressure drops from 38 psi to about 4-9 psi. If i leave it idling for 3 or more minutes and try driving it the xj will go extraamly slow and eventually not move . The only way to drive after that is my consult putting my foot on and off the gas pedal and then the oil pressure will get back to 38 psi and it will drive normal again . Any advice ? The oil is full.

 

It is normal for oil pressure to be low when at idle and warmed up. however the fact that you need to pump the gas pedal to get her moving after an extended idle indicates a possible problem with the injection system. I am not real good at this, but one thing to suspect is the manifold vacuum sensor ( and of course assuring you have good vacuum)

Run a vacuum test, and diagnois from there.