Pedal position vs. commanded TAC position weirdness

[GMPX]

I'm not sure about 5 throttle modes, but there is a series of tables that map the pedal position to blade opening, we don't modify them. It's a little more complex on the E38 to do that than the LS1 was (we did allow it in them).
Normally the response tables are changed by the driver, such as 'Sport Mode' etc, I don't think the ECM determines what response map it uses.

[gmtech16450yz]

Modes of Operation
Normal Mode

During the operation of the throttle actuator control (TAC) system, several modes or functions are considered normal. The following modes may be entered during normal operation:
• Minimum pedal value--At key-up the engine control module (ECM) updates the learned minimum pedal value.
• Minimum throttle position (TP) values--At key-up the ECM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position.
• Ice break mode--If the throttle is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
• Battery saver mode--After a predetermined time without engine RPM, the ECM commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.
Reduced Engine Power Mode

When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
• Acceleration limiting--The ECM will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
• Limited throttle mode--The ECM will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
• Throttle default mode--The ECM will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
• Forced idle mode--The ECM will perform the following actions:
- Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned off.
- Ignore the accelerator pedal input.
• Engine shutdown mode--The ECM will disable fuel and de-energize the throttle actuator.

These are "failure" modes, but I think what I'm seeing is the computer putting it into "acceleration limiting" mode at times. (?) This is all GM gives us as far as an explanation of what happens, pretty vague. I have no way of knowing what they mean by "acceleration limiting", like how severe is the limiting or is it a minor step before it sets a DTC and light and shuts the pedal down all the way?

This is different than the user switchable modes you mentioned, but the computer may be using some sort of these modes automatically when it sees something it doesn't like, like too much airflow.

I don't know of any E38 cars or trucks that have a user controlled mode switch. If there was and by chance it was hard wired into the E38, that would be something I'd like to look into. Have you seen any tables or checks on when and how it does the idle learn? I'd like to be able to turn off the idle learn, I believe it would solve my "low throttle" problem and probably wouldn't have any adverse effects.

Thanks Ross.

[Highlander]

To disable idle learn zero out the correction tables for the idle section.

[gmtech16450yz]

To disable idle learn zero out the correction tables for the idle section.

Awesome! Now we're talking! Thanks Highlander. That's what I was hoping for, someone to come along and mention something I haven't tried yet. I never thought about if it never corrects, it can't "learn" what to correct to.

I have tried reducing the correction tables quite a bit, and did turn them all off when I was getting the base idle nailed down, but they've been back pretty much to stock for awhile now. Next time it gets into that "low throttle" mode I'll turn all the corrections off, do an idle learn reset and see what happens.

What about B1601 and B1602 (airflow correction coolant and baro tables)? If I left those on at least I would still have a little cold start and altitude control. Do you think it will still try to do the idle learn if those tables aren't zeroed also? I guess I could just start with everything off and if it fixes it I'll try adding back in just those tables and see if it relearns to the low throttle mode.

Thanks again, I'll let you know if that does it.

[gmtech16450yz]

Oh well, so much for that idea.

Zeroed out all idle correction tables and the "low throttle" mode popped back up after a couple days. Dammit I wish we had access to whatever controls the pedal/throttle mapping. Or I wish I could figure out what the ECM sees that it doesn't like to put it in this mode. Same tune, a couple days driving, maybe a dozen logs and it will be in "low throttle" mode once or twice with no rhyme or reason why. It will stay in whatever mode it's in during the entire trip or log, it has never switched from "normal" to "low throttle" mode in the middle of a log. It's "learning" or switching into this mode on start-up. Why dammit?!

Ok, here's an idea, I will PayPal $100 to the first person that nails this for me. Tell me why it does it, what to turn off or on to stop it from doing it, or provide me (us) with the tables to control this. (Ross, Paul?) Basically help me figure out how to keep my truck from going into this "low throttle" mode and I'll send you $100.

Thanks