Pablo

iTrader: (1)

this is a 7747, pretty big cam

I could never get the idle right. THe IAC always caused a perpetually high idle... To bring it down i had to set minimum idle way too low which killed my fuel atomization
So I started messing with a few parameters in the chip

the time delays for the IAC retract and extend
The IAC position vs coolant temp
IAC kickdown steps
IAC position vs baro at reset

I reduced the IAC steps vs coolant table but it still seemed like there was no difference
I read that it helped to slow the iac retract and extend commands slightly so I did that. I think I ended up with what is stock in one of the 454 bins
still no difference
Finally I reduced the steps in the IAC position vs baro at reset and it did the trick right off the bat. THe idle stayed low even with a high minimum idle so as to keep the velocity past the tbi butterflies up.

Im coming back to revisit this because its still not right and maybe i went about it wih the wrong course of action.

When i first start the car, cold startup, the idle oscillates wildly from the flare up speed down to near stall then back up again then usually stalls out.. i start it again and it does the same but will usually level off at around 900 rpm and idle pretty smoothly. ONce it warms up it idles about where it should although its not perfect as it surges some.

Im thinking i should start over with the stock settings but then I dont know where to start again. I dont want the engine to idle at 1000 rpm so i need some way to keep the iac from going nuts and opening up all the way. But I need to have it start cleanly and idle smooth from the getgo. It seems like reducing the iac counts made for the IAC to kick down too far on startup and almost stall thus triggering the stall saver.. and once it decays out it almost stalls again.

Ive also been reading that i want the iac counts near zero.. how can I accomplish this? It seems like the only way is to eliminate steps from all of these tables drastically or else it idles high if i set the minimum idle too high

I know im a little disorganized but I just need like a plan of attack as im not sure exactly how each table works

FastBroker

Sounds to me like you may have a VE (and/or openloop-AFR) problem(s) at your desired idle RPM and MAP areas. ie, too lean. What is scan tool saying, if you can get one?

Also, it will be a little tough to get stoichiometric idle with your 214/224 cam on a 305 with your Torquer II single plane. The overlap/reversion/EGR effect are preventing it. your ECU corrects the fuel mixture on the WARM engine running all funky from the non-attainable stoich AFR at idle and sets a funky BLM at that range. Then, when cold at start-up/idle, the set BLM effects the AFR table and makes the actual needed AF ratio wrong.

I hope this makes sense. Your single plane manifold and alternating injectors pulses aren't helping anything, either.

Let us know wassup with your BLM's. Also, where is your spark at idle? You'll need quite a bit more than tock but ai am sure your're pretty high. just don't go too high or you'll get hissy fits similar to what you are seeing.

Grim Reaper

Pablo, I had a similar problem with my idle, except my idle would begin initially too low (inspite of my setting the desired idle speed higher) and then it would slowly increase to the proper rpm. This was inspite of perfect 128/128.

While a scan tool would be helpful, you can adjust for this without one. I found that I had to increase my IAC counts at various coolant levels (I chose the IAC count that my scan tool "settled at" when I got the proper idle after stopping each time). This did the trick and now when I stop the car and go into idle, it idles EXACTLY where I want it. BTW, the final IAC# is usually within +/- 2 counts of my settings.

So, you should experiment with the IAC counts vs coolant temperature; in your case since you are too high, you would want to decrease it. Try changing it by 5 until you get an "initial idle speed" that is close to your desire idle speed.

Also, on my 7730, the IAC has a temperature range for "learn mode". I found that it was not low enough to compensate for my 180* t-stat. I am not sure if an equivalent low/high temperature setting exists for IAC learn on your ecm, but check it out.

EGR has no function at idle as it should be turned off. I did find that when "starting" from a standing start at "part throttle" that I had a "surge" when the EGR kicked in. I did various experimentations and found the BEST setting for the EGR (not sure if you have one) was to set it at the lowest TPS% possible (it also eliminated a "surge" when driving on rolling hills causing the EGR to kick on and off) and altering the EGR machine code to test based on minimum MPH instead of minimum MAT. Basically, I make my EGR turn off/on (no matter what TPS% except when I hit 80%+ TPS) at 8 mph. This gives me a NICE part throttle transition on the EGR from a standing start.

I found this much better than the stock method GM used to control the EGR.

You may wish to check your "Stay Alive Mode" (SAM) for your IAC. Again, mine was too low.

This should put you on the right track to getting a nice idle. It did for me.

[This message has been edited by Glenn91L98GTA (edited April 11, 2001).]

Pablo

iTrader: (1)

a few things
im around 20 deg timing at idle
I have closed loop disabled for the time being
The warm idle is pretty much fine.. just a slight surge. O2 is a little rich.. which is where it kinda needs to be to idle well

I cant get any readings from anything when its cold because the 02 isnt warm enough yet, and, it didnt do this before I started messing with the IAC steps. It would start up.. idle real high, and come down some but would generally idle at like 1000 rpm even if i set minimum idle at 500 rpm
I had to kill off a bunch of steps from everywhere to get the idle to come down, it would sound like the motor was fighting to keep the idle down and would just give up and would idle high.
Glenn, with the tbi its further complicated by the fact that air past the throttle blades is a neccessity since thats what atomizes the fuel. When the IAC was opening so much the rear cyls were extremely rich while the front ones were lean. the plugs look much more uniform now. So its liek a balancing act here I have to remove a ton of iac steps but I have to get it to fire up off the bat when its cold

Ive been looking through a bunch of bins and I found one of the 5.0 man. bins has substantially fewer iac steps everywhere (but more than what i currently have) and im gonna start off with that see how it runs and just slowly kill off more steps if it wants to keep idling high

FastBroker

Are you sure you don't have a vacuum leak????

Pablo

iTrader: (1)

Positive

Grumpy

On my own stuff, I like a 0 IAC at idle. So I set the min idle speed so that the engine will just idle, without stalling. Then noting that rpm set the idle speed to right at that speed, ie on the GN idle speed is 675 (in gear), and has a commanded 650. Course some cars won't idle down smoothly at this rpm but my car does.

Once I have hot idle right, then I slowly back up on idle cold rpm settings. Then the max IAC count.

On several early 747 work arounds were using an electric drill and file to make a less sevrer taper.

Pablo

iTrader: (1)

ah, thanks Grumpy. I had been doing it the other way around which was setting the minimum idle just under the commanded idle.. stupid of me I should have been thinking more about what the engine wanted than what i wanted to force on it.

Anyways I think i have this cold start up idle figured out! I think it might stem from my BPW being set too low so the commanded choke and afr in crank commands were wrong (so yes fast broker you were on the right track). I looked around at some other bins and found that same 305 man. bin had a richer choke and afr in crank. Put it in and the car fired right up.. not perfectly smooth but it wasnt oscillating wildly. Its much much better just has a heavy lope for a few seconds then smooths down. It also took far fewer cranks it was almost instantaneous.