So, I just bought an S2000 literally a day ago, and I noticed something strange. Whenever I turn on the car, I feel the floor (by the pedals) thump. It's like a reoccuring thump. It feels like a sublte feeling when accelerating from 0 on a second gear. For example, I listen to the car, and I hear "thump...thump thump thump...thump"

Sorry for my weird explanation, I'm new lol

Has anyone ever ran into this same problem?

 

It started with the car randomly having a rough idle with the muffler amplifying low frequency sounds. The rpm's would drop from 1k to 800 and back up and I could feel the floor shake a little. I got misfiring codes for it (P0301,2,3,4, and P1399). I thought it was the spark plugs so I swapped those out. It made the sound less subtle but it's still very noticeable. Then I'm at the point that I believe it's dirty fuel injectors. So I'm in the process of using Sea Foam to clean the fuel injectors. I've gone through 2 so far. I'm on my second one. Since I've been using it, I've had less misfire codes. I got a code yesterday for just P1399. Now I'm on the second tank of Sea Foam and I haven't had any codes. The only problem now is that it seems to be clearing up the codes but the rough idle is still present.

Edit: I got all the codes again..

The car sounds very similar to this in the rear...
http://www.youtube.com/watch?v=i5wKBdQPccU

 

I don't know if this is it, but check your motor mounts. The rubber can dry up and crack resulting in the engine bumping against the metal retainer.

 

You may need to buy new fuel injectors to actually make it go away completely.

See this thread...

https://www.s2ki.com/forums/index.php?showt...0&#entry5592292