MoTeC Global Forum

All,
I'm doing some street tuning trying to improve the drivability of the car. What I have notice is, in between gears, the rpm doesn't comes down quick enough. For example, let's say I'm in 2nd gear closing 4k rpm, when I let go of the throttle and engage the clutch in getting ready to switch into the 3rd, the rpm doesn't come down quick enough. It stays at 4k rpm and slowly decreasing when I engage the 3rd gear. Things seems fine but just thought the rpm didn't come down quick enough.

Which part of the tuning should I work on to cure this symptom?

Thanks
Andy

It may have to do with not having an idle air valve controller and the throttle body is not 100% close when the foot is off the pedal. I wonder if there is any tuning trick which can address this.

Log idle valve position to see where the valve sits at 0% TPS but outside of the idle control range.

In idle control menu there is a "initial Position" parameter. Set this to a duty cycle sufficient to fully close the valve when outside of the control range, use the same value as the minimum duty parameter.

Overrun fuel cut would easily override any "air leak" issues if that was the actual cause.

Steve, thanks for the input but I don't have idle air controller on my setup.

mr2andy wrote:Steve, thanks for the input but I don't have idle air controller on my setup.

No idle speed control valve ?

Either wayl, overrun fuel cut will resolve the problem. Set it to restore at say 2-2500rpm. So close throttle anything above that rpm, and a full fuel cut will occur. The engine rpm can do nothing other than fall.

On some cars there is a small throttle kicker that is vacume operated to hold the throttle open see if your car has one.

What type of DBW throttle body do you have?

It's not DBW. It's a mechanical throttle body. It currently doesn't have idle air valve/controller on the setup but I do plan on adding one in the future.

I have read more about overrun fuel cut, is it really suitable to use for in between gear?

mr2andy wrote:It's not DBW. It's a mechanical throttle body. It currently doesn't have idle air valve/controller on the setup but I do plan on adding one in the future.

I have read more about overrun fuel cut, is it really suitable to use for in between gear?

Every OEM car uses this, and most aftermarket.

It is generally for emissions and fuel economy. But as long as it's operation doesnt give you any noticeable bad feelings, then use it.