JEEP CHEROKEE TIMING

Does The 4 Wheel Indicator Lever Always To Be In The 4 Wheel All The Time Or Can It Be In Neutral?

I Have Only Just Bought The Jeep, It Shakes So Violently That It Is Impossible To Hold A Steady Course. I Have To Stop, When I Start Again...

What Would Cause A 1993 Jeep Grand Cherokee To Stop Firing And Getting Gas At The Same Time?