Desired IAC vs Actual IAC

[JoshH]

My dad recently acquired an '06 Silverado with a blown and cammed 4.8 in it. It had some tuning issues that I have been trying to straighten out. Unfortunately, I have no idea what I'm doing :bad:

So anyway, one of the problems it had was it didn't want to idle properly. I've worked on it some after reading some of the idle tutorials, but it still hunts up and down and occasionally dies (usually during slow speed maneuvering). Tonight, I was driving and came to a stop light. The thing would drop down to about 500 RPM and then shoot up to over 1500, then fall back down and shoot up over and over. It was pretty obnoxious. When I got home, I hooked up the scan tool and did some logging. I was logging several different things, but one thing I noticed seemed a little strange. The Desired IAC position was around 75 counts, but the IAC position was showing to be 310 counts. I have logged IAC position a couple of times, and it is always exactly 310 counts and never moves. The TP % will move up and down as the idle goes up and down. Can anyone explain what the IAC is supposed to do?

[JoshH]

One more stupid question. The truck is a 5 speed manual. As I look through the different idle tables, I notice it has different values for drive and park/neutral. It many of the descriptions, it says a manual is assumed to be in gear unless the clutch is depressed (which makes me assume it thinks it is in park/neutral when the clutch is depressed). The thing I'm noticing is just about every P/N table I have seen is zeroed out. Which tables does the PCM use when the clutch is pushed in if the P/N tables are all zeroes?

[WeathermanShawn]

Josh:

I have somewhat moved away from intense online problem-solving of Idle problems..so many variables and quite frankly a lot of Idle problems come from Tunes/Set-ups that are so far from stock.. that solving them become very difficult.

So, I may not be a lot of help on your specific problem. But, one aspect of your question I might have some insight. One user stated the following concerning Airflow issues with a Manual and the clutch-pressed.


I had a problem in my FI/cammed/M6 car where the RPMs would hunt from 500-1200 whenever I pushed in the clutch after being in gear. Like when rolling up to a traffic light, push in the clutch, then the engine would rev up and down by itself. Once at a complete stop, it would settle down to a steady 850rpm idle.

I tried B4309-Throttle Cracker Airflow in Gear (TC) and it did absolutely nothing to solve this problem. Then I did a little experiment and got the car moving, pushed the clutch in, put the tranny in neutral and let out the clutch (still moving). Ahhh, the RPMs held at 1200 rpm with no hunting. Pushed the clutch back in and the RPMs started hunting again.

That experiment made me start looking at the B4310 Throttle Cracker Airflow in P/N table. Mine was originally set to all 0s. For grins I set the entire table to 3 g/s. Took it out for a spin and pushed in the clutch and the engine held a steady 1100 RPM or so. A little tweaking of that table to get the RPM where I wanted and reducing it a bit at the lower speeds got it transitioning real nice as the car rolls to a stop. So B4309 is only active when the clutch pedal is out, and B4310 is active when the clutch pedal is in.

Might be worth adding to the first post as M6 cars are in P/N much more that auto cars.


So, you might want to look that over and see if it helps..The original thread is found here:http://forum.efilive.com/showthread.php?14439-Idle-Tips-amp-Tricks&p=133946&viewfull=1#post133946

[Sid447]

An '06 Truck,

Isn't fitted with an IAC motor they all went ETC by 2003 or so.
Best guide is to compare the tune file with a 5.7 or 6.0 with a manual box there's plenty on Holdencrazy.

[O1Z06]

An '06 Truck,

Isn't fitted with an IAC motor they all went ETC by 2003 or so.
Best guide is to compare the tune file with a 5.7 or 6.0 with a manual box there's plenty on Holdencrazy.

Yep, definitely need to log IAC_DES_B (g/s) for ETC and IACDES (steps). Probably want to get WO2EQ and GM.EQUIVRATIO in the ball park with BEN then make a DYNAIR (g/s) map and throw that in your {B4307} desired airflow table. See how it takes to that. Then work on your follower and cracker tables.

weathermanshawn, that brings me to an interesting point about the clutch, I just accept the fact that I make sure to put some, if not the same, data into P/N tables and never leave any 0. However, when logging GM.GEAR, log always shows 3 and GM.PRND always show D4 regardless of clutch position:confused:

[joecar]

GM.GEAR and GM.PRND are for the auto trans only...

You want to look at the Clutch Pressed bit in GM.TSTATE00.

[O1Z06]

Clear as day now, thank you Joecar