My 96 3.8 L will develop a rough idle after warm up. Have determined that the two vacuum motors on left (passenger) side of engine appear to be cause. Q: what is their purpose? They appear to operate a shaft(s) going into the intake manifold. I have disconnected and plugged the motors vacuum hoses and that has somewhat reduced the effect of rough idle. Q: How difficult is it to R & R these motors?

I think you are referring to the IMRC motors. The purpose is to change the intake path to a shorter run at an RPM of 3450 (?) or so. The theory is that long intake paths promotes torque (which you desire at low RPMS) and short intake runs promote hp (which you want at higher RPMs).

I think you are referring to the IMRC motors. The purpose is to change the intake path to a shorter run at an RPM of 3450 (?) or so. The theory is that long intake paths promotes torque (which you desire at low RPMS) and short intake runs promote hp (which you want at higher RPMs).
Thank you for the information. Your explanation helps to understand my problem...

although I don't see why they would cause a rough idle