Abnormal Bucking/Jerking under Partial Throttle
 

Lately my car's been bucking/jerking under abrupt changes in throttle position, ie if I lift off the throttle (but not all the way off) and get back on, the car will buck/jerk back and forth. It's a bit like driving around in 1st gear, but you're actually in 4th.

My friend has an S2000 as well and I drove both cars back to back - there is definitely something wrong with mine.

Does anyone have any ideas what it would be? I suspect engine, transmission, or diff mounts possibly having failed - could all of these produce this symptom? On fluid-filled mounts (all of these are) will it always be obvious upon visual inspection whether they've failed?

My guess would be throttle position sensor.

^
That's the first thing I thought of when I read the thread title, the second was mounts.

On my mounts it's quite obvious when they fail, the rubber web that connects the inside to the outside is ripped. I'm not expert enough to say for certain the s2000 would be the same. If it is the mounts the simple/cheap fix/mod would be filling the mount with construction adhesive to turn it into a solid mount.

Engine mount DIY from S2ki, pictures of broken and intact mounts.
http://www.s2ki.com/s2000/topic/8033...r-motor-mount/

Aside from a visual inspection, you could also load up the drivetrain and and get a friend to inspect all the mounts.

Yeah I guess that should be pretty quick to check.

Hmm. Regarding engine mounts, there definitely aren't more vibrations than usual, and it wasn't sheared off for sure when I took a quick look at them from the top / sides as I reved the motor. I just don't have any experience dealing with fluid-filled mounts - I mean will they actually visibly have torn boots / leak fluid, or can it be more subtle than that?

Any suggestions for how best to do this, other than yanking the handbrake up and sorta slipping the clutch in 1st?

Put it on a Y lift? I won't want a friend to be underneath a car that you are shifting weight and momentum around.. unless well he/she is not really a friend.