slow speed idle flare

[gerry_foster]

Good day folks.

I've got an odd and slightly irritating idle issue on my combo.

Gen 3, LQ9, 243 heads, BTR stage 2 truck, TBSS intake, 92mm DBC, 50 lb injectors, Gen 5 8L90E, 2800 yank pro truck.

in an 87 Suburban.

cold start is great, 99% of drivability is great.

Issue is, operating temperature, idling, say backing up or driving forwards, as soon as it moves a few feet, no throttle input, the idle speed increases aprox 300 rpm and it really makes it want to push against the brakes, it'll hang there for say 3-4 seconds, then drop back to the target 700 rpm. Trailer towing and parking lots are annoying is you have to wait for it to drop back down before changing gears or it is not a pleasant gear change....

any help would be greatly appreciated.

tune and log attached

Thanks Gerry

[HATEHPTUNERS]

What type of 92MM throttle body are you running? I ask because I am going through similar issues, and am now in the process of replacing my TB with a Nick Williams unit... What brand of TB is it?

[HATEHPTUNERS]

Also, you could try logging IDLE air desired, dynamic air, IDLE COUNTS, throttle follower, throttle cracker, and any other airflow channels that you can log that could potentially be active at or returning to idle. If the extra air that is causing that idle increase is not a result of the computer commanding it... What you are trying to find is if that extra rpm increase is a result of something in the tune. If you can't find that the PCM is adding the extra air.... then you will have to look elsewhere. What type of TB are you running again?

[gerry_foster]

What type of 92MM throttle body are you running? I ask because I am going through similar issues, and am now in the process of replacing my TB with a Nick Williams unit... What brand of TB is it?

China el-cheapo unit

[gerry_foster]

Also, you could try logging IDLE air desired, dynamic air, IDLE COUNTS, throttle follower, throttle cracker, and any other airflow channels that you can log that could potentially be active at or returning to idle. If the extra air that is causing that idle increase is not a result of the computer commanding it... What you are trying to find is if that extra rpm increase is a result of something in the tune. If you can't find that the PCM is adding the extra air.... then you will have to look elsewhere. What type of TB are you running again?

Thanks for this idea to scan the airflow adders, i did this just now and i can see my issue i think, my vehicle speed input I'm feeding the gen 3 looks to be SUPER glitchy at slow speeds, moving only a few feet its jumping to 19 kph and the cracker airflow is adding as it presumes im moving a fair pace.... i've unhooked my VSS input for now and ill log without it to see how things improve

I'm running a very odd setup with the Gen 5 trans, so im feeding the Gen 3 speeds that are translated through a dakota digital speed conveter.

Thanks again for the idea, ill post back after another test

[curiousg7]

Your overall airflow characteristics are problly inaccurate. From what you have logged it is desiring a low amount of airflow when stopped, maybe to counteract the difference in the IAC table? I'm not sure.