The engine speed cable installed

Manual Idle Air Control

The ITB idle air control conundrum

Idle air control is generally a challenge with individual throttle bodies.  This is from the sensitivity of throttle position to airflow at low rpm.  An idle air control strategy controlled by the ECU can work but requires a large investment of time and knowledge to tune properly. In the end may not be utilised only on colder days.

I am located on the edge of Australian temperate and sub tropical climate zones at an altitude of 680m over sea level. The ‘cold’ weekends I’d reasonably drive my car are few and far between.  I could likely get away without an idle control method but I wanted something just in case.  hmmm, what could I do?

Repurposing a factory safety issue

The Datsun 240Z I own is an early model complied in April 1971.  It came with the manual engine speed lever meant for cruise control but was removed in many countries.  The solution for an idle control valve was simple albeit not original. Reinstate the lever to allow control of the throttle through the lever’s connection to the throttle pedal.

Installation of the cable was not difficult.  I merely clipped the cable to the fork at the top of the accelerator pedal and clamped the cable in the factory holder and voila!  Some adjustment of the slider clamp was required to resist the tension of my throttle return spring and hold position.  I also installed a maximum throttle stop as a safety measure to prevent accidental excessive throttle openings.  Refer the new screw and washer in the photo below.  The lack of safety is likely one of the reasons the speed lever was removed from production.  The lever was calibrated to a maximum 4.0% throttle and this is perfect for a high idle air control.

The final install complete with calibrated safety stop

This does mean I need to install some sort of support for the lever.  The logical answer is reinstate the factory centre console which I may do in the future.  Right now I am happy I have a functioning low cost and factory ‘look’ solution for idle air control.  The tune for the ITBs is ongoing and I may adjust the stop to suit.  My EFI tune uses Alpha-N as the algorithm and this can sensitive to small changes of TPS at low RPM.

Thanks for reading. Catch you in the next one!

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Manual Idle Air Control

The ITB idle air control conundrum Idle air control is generally a challenge with individual throttle bodies.  This is from the sensitivity of throttle position