I have an LS2/T56 from a 2006 GTO, dirve by wire set up in a 240z. I autocross the car and drag race it just for fun. When I let off the gas pedal, I would like the car to immediately engine brake in order to transfer weight from the back wheels to the front to help me get around tight turns better. I would also like to be able to double-clutch better, but the rpm just won't drop very fast. Unfortunately, the motor just sort of coasts when I come off the pedal. If the car is in neutral, for example, when I rev to 2-3000rpm, then get off, it takes several seconds for the rpm to slowly return to idle. I assume this is some sort of stock EFI anti-polution setup, because my EFI S10 truck does the same thing. I'm used to driving carbureted motors which don't think for themselves. What can I change in my tune (I'll pass this on to my tuner-have an appointment Saturday) to make the throttle snap off to idle when I get off the throttle?

 

what gears are out back?

 

Dfco will help with the engine braking

 

What is Dfco?

 

I think it may be in the idle air control. Once it's hot and idling, try unplugging the IAC valve to test. Don't know about LS systems but it may be possible to program RPM control to force IAC fully closed above a set RPM and not enable IAC control until below a certain RPM. Might also be able to take out excessive timing with TPS closed and RPM above a certain point.

DFCO is decel fuel shut off I think and I've run with it off and on but don't know how much effect it'll have on what you want to do. I would assume with it turned on that timing is advanced when coming off throttle to help lean burn.

 

dfco does exactly what it says. it shuts off fuel. you can change how and when it comes in. should help if you want the nose to settle when off the gas

 

Thanks fellas! I'm to see tuner in the morning. He adjusted idle airflow some, but I don't know how much. I will talk to him about DFCO. do you think I could just disconnect the IAF sensor (assuming this is easy) just as easily as adjusting the tuning? The tuner was worried about his tuning causing me to have trouble with gear changes at the dragstrip. I guess the run-on makes the car feel like it has a real heavy flywheel. Maybe I could disconnect IAF for autocross and reconnect it for drag?

 

if you mean IAC that would probably cause some pretty big drivability issues

 

Completely blew past the fact you're using throttle by wire. There's most likely something that can be done in there although the IAC control can also have some input. I believe even on throttle by cable they buffer the idle down with the IAC. Maybe for emissions?

 

me too

 

Thanks again. BTW-nice avatar Outkast. I'll let you guys know what turns out. Appointment is tomorrow at 8am.

 

They can probably turn off any kind of signal or servo buffering. I know they make a "throttle conditioner" that can be added to cars but don't know if those affect anything besides acceleration parameters.

 

I think we were both too busy thinking about *******.

 

You meant safety harnesses right?

 

Yes. With nipples.

 

Tuner dropped IAF/IAC to zero from 2000rpm and up, and lowered DFCO as much as possible too. Weight transfer with throttle lift is almost instantaneous. Car was super tail-happy at yesterday's autocross. Perhaps too much! Had national champion drive the car (I've been driving this car for 20 years and his second run was a second faster than my fastest time of the day-and way more controlled). He felt the car was neutral in a turn, but that any application of throttle in a turn immediately wanted to spin the car. 435# of wheel torque in a 2400# car with 40 year old suspension technology on discount street tires is a friggin' rodeo! He boiled the tires on any short straight away and got me a noise warning (100dB)! Next tuning change will be to reduce the rate of pedal input in the DBW throttle body. I recall the tuner said it was currently set at 100% fast. I gotta invest in HPtuners. Tuner didn't charge me for yesterday's adjustments. Thanks, fellas for all your help.