Forum » Practical Dyno Tuning » Idle Control with ICV and PID / RPM drops when off the throttle

Idle Control with ICV and PID / RPM drops when off the throttle

Practical Dyno Tuning

Discussion and questions related to the course Practical Dyno Tuning

Page 1

Hey Team!

I have been fighting my idle setting for a while and managed to make the car idle a lot better than ever before. The idle is very stable with minimal oscillation BUT... I am struggling with revs dropping to low when I blip the throttle or when I shift to neutral from higher revs (2k+) and stop at traffic lights. I tried increasing P, I & D, integral limits, feedback % and rpm deadband but I got to the point where it was too much and made things worse. Also, I tried adding or using only idle ignition control and that didn't help, too. The ECU is EMU Classic. Can anyone help? I will be happy to post any logs you may need.

What is the vehicle and engine? Can you post a screenshot of your idle settings? Also, what about your deceleration fuel cut recovery? Can you post a screenshot of those settings? Also, please post screenshots of idle ignition timing.

From the hardware side: A lot of the idle problems are made worse with lightweight flywheel and aggressive clutch design. It makes the revs drop very fast. Also, many engine throttlebodies have a "dashpot" which is meant to close the throttle valve more slowly. Has your throttlebody been modified at all? Also, what adjustment screws are on your throttlebody? Some throttlebodies have an adjustment screw for bypass air + an adjustment screw for the the stop position of the throttle plate.

Sometimes the solution is less spark with more air. Crack open the throttle plate or adjust the air bypass screw to raise the base idle. Then retard the base spark to bring the idle back down. Then raise the fuel cut recovery engine speed setting and use the idle air control valve to catch the idle on decel.

deceleration fuel cut recovery?

can you explain more about this?

When you accelerate from 1000 to 3000rpm, the engine is injecting fuel. When you take your foot off the accelerator pedal and push in the clutch pedal, the ECU reads the throttle position sensor is 0. Usually it will stop fuel injection. As the rpms drop, the fuel injection needs to start back up in time to build torque and keep the engine from stalling. If you re start at higher rpm (like 1500rpm instead of 1000rpm) you will have more time for combustion to keep the engine from stalling, but you don't save as much fuel.

ok, thank you for your answer, this is overrunfuelcut function in some ECU. As allways thank you for your explanation ;)

Hey Drew, did that fix your issue ?what did you wind up doing ?having the same issue

What same issue do you have? And what car are you working in?