I have recently installed the motor mods below, and have been tuning it with EFI Live. I have a LC1 wideband. I edited the IFR table for the bigger injectors, and I have done RAFIG/RAFPN and Auto VE. My desired airflow and AFR seem to be very good. I have adjusted the throttle stop screw to get my IAC steps ~30 or so, and reset the TPS, and adjusted the IAC effective area to the right to get desired/actual airflow close. I also raised my TCC lock/unlock speeds to keep it from bucking at about 1600 RPM when off the throttle. I've come a long way but still have an annoying and persistant problem.

It starts and idles fine, and idles fine in gear. Drives well and has no real issues other than a surge at really low speeds and when coming to a stop. Once stopped, it will settle down and idle fine. But from a stop, if I put it in gear, and let my foot off the brake and let it start rolling, it will do it by itself. It starts rolling slow but gradually gets faster and starts surging. It will keep doing it until I come to a complete stop. Same thing when coming to a stop while driving. I have tried taking all of the air out of the throttle cracker at low speeds, and logging it to verify that it's not adding any. But it seems to be airflow related, because my calculated airflow (GM.DYNAIR) will spike to 17, while desired IAC airflow will be about 10. All without ever touching the throttle. When this is happening, my AFR looks good (gradually swinging back and forth over commanded AFR - 14.63), and my spark curve is not spiking; it's nice and flat. So I think it's airflow but don't know where it's coming from. I've tried adjusting all the learning tables and timers and everything I do there just seems to make it worse. I have my idle set at 850, but have tried it all the way up to 950 and still have the same problem. Where is it feeding it air from with my foot off the gas if it's not the cracker?

Any help? Thanks in advance.

 

Try messing with the idle and main spark table. You might have a bit too much spark advance in low rpms.

I'm a tuning newb but it's just a thought.

 

Thanks for the reply. I have actually already pulled a bunch of timing out of it to get it to idle without surge. Now it idles fine when stopped, but not when rolling slow or coming to a stop without my foot on the accelerator.