it is probably for emissions purposes i could see that.. the car hangs even worse when the car isnt warmed up. on a cool morning start your car up wait 30 seconds or so drive off and take a look at everytime you shift it will hang longer and even rev up slightly everytime you shift when its not warmed up.

not necessarily for emissions, but the ECU holding the RPMs to make sure the fuel is burnt and such makes perfect sense.

Here's my take: It is the modern, electronic equivalent of the old decel controls on carbureted engines. Meant to control emissions on deceleration when throttle is fully closed.

US Patent 3957022 - Carburetor deceleration emission control



Description

This relates in general to a two-stage motor vehicle-type carburetor. More particularly, it relates to one that is provided with suitable apparatus for cracking open the secondary induction passage throttle valve during engine deceleration conditions to improveemission output.

This invention has particular use with four barrel truck-type carburetors, although it will be clear that it will apply equally as well to any carburetor having dual stage operation. In a four barrel carburetor of the type describedhereinbefore, the conventional idle provides a quite lean mixture to the engine cylinders. During closed throttle deceleration operation, therefore, the engine will be provided with a very lean mixture to the point where incomplete burning mayoccur, which may result in unburned exhaust gases and the emission of undesirable into the atmosphere. If, during this time, fuel and air is added to supplement the idle system mixture, then a more complete burning of the mixture may occur. The addition of fuel alone generally is not sufficient but both fuel and air should be added to provide the proper mixture ratio.

Accordingly, it is a primary object of this invention to provide an engine deceleration control apparatus incorporated in the carburetor that operates during deceleration conditions when the primary and secondary carburetor throttle valves areessentially closed to crack open the secondary induction passage throttle valve to supply a quantity of both fuel and air mixture to the engine to supplement that mixture emanating from the primary induction passage.

It is another object of the invention to provide a four barrel carburetor with a vacuum servo connected to the secondary induction passage throttle valve and operable during predetermined deceleration conditions to crack open thesecondary throttle valve to allow the induction of an additional air/fuel mixture into the engine.

It is a still further object of the invention to provide a four barrel carburetor construction having a servo operated secondary throttle valve system with an additional vacuum servo that is independently operable during predetermined enginedeceleration operating conditions to crack open the secondary throttle valve to allow the addition of air and fuel to the engine regardless of the position of the primary throttle valve and quantity of flow of mixture through the primary inductionpassage.

It is another object of the invention to provide a four barrel carburetor construction having primary and secondary induction passages each provided with a separate throttle valve rotatably mounted across the respective passages to control theflow of an air/fuel mixture therethrough to the engine cylinders, the secondary throttle valve being opened to provide greater air flow capacity to the engine during engine acceleration conditions by means of a vacuum servo connected to the throttlevalve and operated in response to a vacuum signal in the primary induction passage venturi at the appropriate time, an additional vacuum servo being connected to the secondary throttle valve by a lost motion connection and operable in response to theattainment of both a predetermined engine speed and vacuum level condition to crack open the secondary throttle valve to permit the induction of an air/fuel mixture through the secondary passage to supplement that flow quantity being supplied to theengine by the primary carburetor section, to render the engine air/fuel mixture burning more complete and thereby reduce the output of harmful emissions.

It is a still further object of the invention to provide a carburetor of the construction as described immediately above in which the second servo is actuated by vacuum as controlled by a solonoid actuated valve that iselectrically actuated in response to engine speed and manifold vacuum both rising above a predetermined level.

Carburetor deceleration emission control - US Patent 3957022 Description

^ Good info. +rep

Lmao I was eating lunch and reading through the whole thread and your last paragraph almost made me spit out all the food in my mouth. :) and yeah I definitly do feel a throttle delay compared to my g35c. I can slam the accelerator down and there's a heavy delay. The g35 was very sensitive. I loved it.

We're not talking about a throttle delay :ugh2: Is your G35 a 2004.5 model?

:facepalm:

I know you guys are talking about the throttles rpms hesitating to go down once you let go of the accelerator but didn't someone also mention about the accelerator being delayed also? I might just be going crazy lol but my g was a 2003.

Yep this was one of the first things I noticed when I first got my 350. I think its by design. The reason I say that is because in all my previous cars, if I was rolling on 1st gear and then dropped the pedal it would jerk back and forth. But in the 350 you could roll in any range of 1st and drop the pedal and experience little o no jerking. I think it was designed to allow for a smoother ride when dropping the gas pedal at high rpms.