Alright having a bit of a problem here. First off, here are the modifications made that could play a role in my problem.

I am boosted
street tuned w/hondata s300
blox throttle body
skunk2 intake manifold
DSM INJECTORS W/ RESISTORS NOT YET INSTALLED
walbro fuel pump

Heres the problem...
while in gear, if i let off the gas, my car will start decelerating quickly, and abruptly (as in it jerks my body forward a lil bit) for a split second then start decelerating like it normally should when you are in gear but foot off the gas.
it doesnt happen at any particular RMS, speed, or anything. like for example, say I'm in 3rd gear going 30 mph with my foot on the gas and its only a 25 mph zone so as I pass an intersection to be safe I take my foot off the gas to make sure I dont go any faster/slow down a lil bit (still in gear) and normally I should slightly and pretty smoothly start decelerating. Instead, the instant I take my foot off the gas, the decelerations starts so quickly my body jerks forward.

now I'm not saying the actual deceleration is so abrupt that if I didnt give it gas or shift to neutral that I'd come to a complete stop within 5 seconds or anything..... but like the transition from my foot being on the gas while in gear to my foot being off the gas in the same gear makes the whole car jerk (best way to describe it is it feels like someone quick slams the brakes for a split second) .... then after this herky jerk occurs, the deceleration occurs at a fairly normal rate.

it's just (while staying in the same gear) the instant I let my foot off the gas the car for a split second has an abrupt, rapid deceleration......and then when I hit the gas after this, its the opposite, its like an abrupt, quick split second burst of acceleration.

 

my 2nd gear is like that, sorry i'm not help but i'm curious about it too

 

Maybe the throttle body isn't letting the air blow past it when the plate is closed like it is supposed to?

Or my other idea, not to insult you or anything, is a lesson in driving a manual 101. Don't just jump off the gas, let the pedal out smoothly and it shouldn't jerk as much.

Is this a post boosted problem or has this always been happening?

 

my car does that all the time havent seen a real problem yet it just shakes a little when you let off the the gas then it decelerates like normal.