My 1998 Civic DX with 140k and a manual tranny miles jerks HARD once when starting acceleration (e.g. going from coasting down a hill to driving on flat) or when moving from coasting to acceleration (e.g. cresting a hill and taking your foot off the gas). After the jerk, it drives normally. It had a mild jerk for several months, then I stored the car for a year, and now it is a driveability issue: its serious enough I'm worried about harming my engine mounts!

The jerk seems to occur at a particular position of the gas pedal.

Maybe my TPS has a flat spot?

OR

Could this be a symptom of a worn clutch?

OR...?

In case its related: another issue appeared when it came out of storage, the car high-idles normally when warming up, but once its warmed up, it cycles between a high and low idle once a second. Very annoying, and probably bad for the engine.

Thanks a ton!

 

The idle issue is probably your idle air control valve... Should be on the back of your intake manifold and has two coolant lines ran to it... remove the 2 or 3 bolts, unclip the coolant lines and spray brake cleaner into the iacv. The jerking sounds like your motor mounts are already shot... pop your hood,set the parking brake put it in gear and let out the clutch slowly while giving it gas. This will create torque and have a buddy watch your engine... if your engine looks like its rocking alot or lifting up too much, your mounts are probably shot...