Why would a 1998 subaru impreza non turbo manual be jerking while driving

Does it throw a misfire (PO30x, x=1-4) code after scanning the CEL? Look for a wet (too much leaked oil) plug, bad wire connection, wire shorting to intake manifold (very common), or, lastly, bad coilpack. If ignition checks out check intake plumbing for leaks or loose connections allowing lost vacuum. Lastly, remove plenum and spray-clean and scrub throttle body guts before spending bucks. You might check EGR or PCV, but they're usually ok. Water in gas'll do it, too, so make sure you NEVER drive below 1/4 tank full with such an old gas tank. Report abck! Ern