Subaru Repair: Random jerk at high speeds, cylinder misfire, secondary ignition

Question
Hello,

Year 2000; 110k mi

For the past 5 months or so, I've noticed a very RANDOM jerking with the car at high speeds.  When I say random, I mean random.  I could drive the car for two hours down the highway and not feel a thing.  Other times, I'll feel it jerk for a split second.  It only seems to happen when my foot is on the gas pedal.  It also SEEMS to be a little more noticeable when going up or down a steep hill.  When it jerks, the engine does not seem to lose any power, nor do any codes come on. It's almost like something was out of whack and is "jerking" back into place.  There are no grinding / clicking noises anywhere (suggesting it would be a bearing).  I've replaced all four shocks/struts, replaced two front driveaxles, had it professionally aligned, replaced tranny fluid & plugs/cap/rotor/wires about a year ago.  I am really at a loss and was wondering if you might be able to help.  Thanks so much.  Joe

Answer
Joe,

You are all over the map in regards to what you have tried to deal with the symptom.

A "jerk" would usually be related to a primary or secondary ignition issue.

It could be anything from a relay to a spark plug and involves a process of elimination by diagnoses of suspected components.

Not sure about the cap and rotor as your 2000 Subaru does not have a distributor.  Also the jerk could be a cylinder misfire and it may not set a check engine light if it is that random due to the programming of the computer and it may never recognize the problem and thus not set a check engine light.

Justin