IAC question: Why did GM use delays in the IAC extend after an IAC retract command. It causes a 'rpm hang' after a throttle blip or throttle lift and it's getting on my nerves. Like if I try to get out of the way of some jerk on the road but then have to get hard on the brakes because the guy in front of my (typical Ohio driver) doesn't turn his indicator on and I almost run into him. This delay in the IAC closing is making fast acceloration and immediate stopping near impossible. I'm not a wreckless driver and have a clean record to prove it, I just sometimes need to use my car to change lanes and avoid accidents.
What is the purpose of the IAC lag delay?
It's very noticable if I just blip the throttle at idle and it's just plain dangerous when I need to slam on my brakes (but the engine RPM stays too high)!
Oh yeah, this might not be such a problem if I had a higher stall converter...but I don't and it won't be installed until this summer.

 

If you stalled when slamming on your brakes, you would lose power steering and power brakes. It seems more like a safety feature than anything.

 

I know on the manual cars it was supposed to aid in shifting. The RPM hang makes for a smoother shift.

You only appreciate it if you don't have it. In my 5.0 Mustang I have a T5 and the original ECM which was for an automatic. You either have to be real quick on the shift or let off the gas way late to prevent giving yourself whip-lash.

 

EZ fix,
just neutralise the throttle follower stuff in the chip.
Oh, BTW, don't even try to drive the car. You'll quickly see why part of it is called Stall Saver.

Defensive driving is what the chips are designed for, not for folks that tailgate. Assured Distance prevents having to get hard on the brakes.

If you want to customise the chip then fine, do away with it. Oh BTW, the $3,000 FUEL and most other aftermarkets ecms use a throttle follower.

I often don't use signals when someone is tailgating me <g>.
I also, tend to slow down 5 below the speed limit too.

No officer, I wasn't racing,
that was just a pace lap......

 

Wow, Grumpy drives without indicators. In NJ that's illegal, it's called wreckless driving since you don't give on coming or following traffic an idea of what you plan on doing in the near future.
The situation I was describing in my original post:
I was in the left lane on High street and it's 2 lanes both way. I was following 2 guys and I was in the left lane. The jerk put on his indicator at the light when there was LOTS of oncoming traffic and he didn't even attempt to get into the middle turn lane, he was half and half. Okay, no problem, I was far enough away from him that it wouldn't be trouble stopping or getting into the right lane to pass. Well it turns out that while I slowed down, changed lanes and proceded to accelorate to get into the left lane again, the guy I just pulled behind slows down to an almost dead stop to turn right into a parking lot of a CVS pharmacy. He didn't give any prewarning. It would have been his fault if I had run into him but I didn't since I'm just THAT GOOD . I don't like taking chances with my car, my life, or my money, so I am a very good driver (only tailgate when I need to). I just want people to use indicators the way they were ment to be used. I don't care if you gotta use your hands out the window in the freezing rain, DO IT!
I'm not sure about Ohio but in the city, if you don't use your indicator you'll see a big middle finger in your rearview and hear my horn. Remind me to never follow you anywhere when I don't know the directions. Or have you never seen "traffic" like 90% of the Ohio drivers. Take your "defensive driving" tactics into NJ and you'll see something called roadrage. I don't have roadrage, I just get upset (without loosing focus on the driving) and considering I've yet to be in an accident I think I'll just dismiss your reply as an attempt to convince the rest of the members that I'm a tailgater.
Nothing bugs me more than a driver that doesn't use all the tools availible to him/her to prevent accidents. It's ranks up there with my drunk drivers and sleepy truck drivers.
Use your indicator and maybe there wouldn't be a need for such paranoid driving tactics. I respect the whole x car length away from the car infront of you but sometimes that isn't possible. If you told me you've never tailgated I'll call unless you can prove you've never been to a city.
If you want proof on why tailgating is sometimes the only solution: You're driving down a road in heavy traffic and there are *******s driving up the curb/shoulder/turn lanes and cutting in front of you unexpected and if you run into them it's your fault. This is , so I usually stay very close to the person in front of me because nothing is more dangerous then allowing chaotic drivers to have their way. Never will I be so kind and let those self centered ****s have their way!
Now back on topic, why would the car stall if the DFCO and min idle was tuned accordingly? Too much fuel could be corrected with the DFCO values and nobody said the IAC should stop working, I just said it should close at a faster rate, it's a car, not a boat!

 

I don't tailgate - too many crazy drivers that sometimes have burnt out tail lamps or brake suddenly for halucinations.

Yeah, it's an absolute pissoff when you are leaving a "saftey margin" behind the car in front of you and some jerk cut's in. But rear-ending someone and having my insurance premiums go up ticks me off even more.

I think there should be a DIY project to develop a "ray" that sends a strong electronic pulse signal to fry the jerk's ECM. Less messier than the Sidewinder Missle Project I was working on. I never could figure out how to reduce the shrapnel hitting my car.

 

So, back to IAC/throttle following habits of ECM's, what I don't understand is why they are so darn important? My 71 RS has a carb on it, and it surely doesn't have a ECM, or IAC, or any other ways of controlling air to the motor other than my right foot. It is just fine that way? I never had any problems shifting it, and it's a 4spd car....
Isn't the throttle following just a bandaid for someone who can't actually drive a stick? (no flame intended here)

 

Wreckless, or Reckless?.
Hahaha, give it a break.
BTW, I thought people were only sentenced to time in NJ.

Anyway, read up on the throttle follower stuff, and you'll have the answers.

 

I think changing the filter constant is the best way to go (as mentioned above). As for the carb, it has a built in throttle follower. That is why you don't have problems with it. The ECM has an adjustable one. It can be tuned for driver preference.
J

 

How do you figure that a carb has a built-in throttle follower? There is no IAC, or any other variable air-bleed device, on a carb. When you let off the gas, it returns to idle.

 

Yes, you are right that they don't explicitly have a device on them that is creates a thorttle follower. From my experience they are slow to respond when releasing the throttle. That is all I meant by it. I don't have anything to back it up with..........just my limited experience.
J

 

oh.

well, my experience is limited too i guess, i've only driven one carb car extensively, a warmed over ~330hp smallblock 350, and it definately did not hang the throttle at all. if you took your foot off the gas, it was going to idle, in a hurry. it's really no different if the throttle blades are hooked to a carb or a TPI throttle body....no airflow is no airflow

 

It's not that simple. The IAC is a vacuum leak that lets air pass the throttle blades. It basically gives the ecm control of your engine speed to an extent. Obviously it can't rev the engine to 5 grand but it doesn't have a problem getting it past 2000 even if your min idle was set to 500. I'm going to fidle around with this thorttle follower stuff when I get home for spring break. I know it isn't that big of a deal but it's dangerous with my low stall tcc. Just today I had my brake down HARD and I just gave it a little big of throttle to load up the tcc, well I guess my tcc is super tight because it didn't take much throttle to start burning out. I had my door open and I was just looking at the tire turning on warm pavement! I really hope I get to do the cam swap this summer, gives me a reason to pull the engine and install the higher stall speed tcc.

 

one word-emissions-also, the idle flare on start is there so the converter and o2 wake up a bit sooner. dashpot? familiar with it? 69 road runner of mine factory 4spd 383 original avs carb -440 six now though hehee-had that there device on it-whut fer? to keep the throttle blades from slamming shut accompanied by the belch of unburnt fuel (hc) out them shiny oval tips. it only allowed a gradual closing to curb idle starting at around 1100-1000 rpm. gm has the same type of operation in mind with the programming concerning the iac. seems to me that some other factor is amiss in your car, to be experiencing that to the extent you are.

 

Ugh, right
Higher Stall TCC?.

 

ahhhh....last time I checked the TCC had nothin to do with the stall speed..

 

damn cut the guy some slack he asked a tech question he didnt ask for his driving habits to be put on trial

 

pablo-it does seem to me also that one must tread very lightly whilst visiting this particular area of thirdgen. i feel much more at ease in the other forums, where it seems that most questions may be asked, without fear of being publicly mutilated, but again, its only a feeling. only me, just my perspective. :hail:

 

Maybe me lingo isn't as good but last time I checked the stall rating of a tcc has everything to do with the stall speed of an engine. A higher stall would give me a little more rpm to work with because it's either designed for my engine or looser = less power to the wheels because it slips a little more that a standard tcc. This stock tcc is just too tight right now, it's really dangerous with the way my tranny shifts and my small tires.

 

dude...the torque converter clutch (TCC) only controls the actual lock up of the converter not the stall speed. The stator and turbine design, eg number of fins and angle determine the stall. In addition the engine itself along with the torque converter play into the final real time stall speed.

 

Sorry for the mis understanding, I just say tcc when talking about torque converters in general, I didn't know it was so specific. I always just say tcc when I should probably talk about the stator and fins and jazz.
edit: http://www.ag.auburn.edu/users/gparmer/efi/glossary.htm
I should have read the definition more closely.

 

I was wondering about this too, as when I did the obd1 conversion in my 4th gen, it is to a point where I find it annoying. It feels like the pcm is trying to drive the stick for me. When I am decellerating, the pcm feels like it is trying to match revs with engine speed, I think this is great except below 1500rpm where I spend actual loaded time in 6th gear, the IAC tries to accelrate the car even if I don't want it to. It doesn't succeed, just makes annoying backlash noises in the rear end as it wins and looses. It wasn't as severe before the conversion, and I have yet to find a defined table in the pcm that allows me to alter it. I use tunercat, and haven't found this yet. I can't stand it.

 

stangeater-im swapping an 870 to a 730 soon. in my endevour to really throw as many potential mishaps in the recipe as i can, im installing a richmond 5 speed in place of the 700 right now-waiting for the balance shop to finish up the flywheel and fluidamper- and have wondered about this potential driveability snafu. to the point of checking the 8d mask to try and id the parameters that could influence this idle up pita-in the constants i have found "add to idle in park/neut.", "iac command speed open loop offset", "maximum vehicle speed for idle", "maximum %tps for idle" have you any similar tables in the lt1 program? tried them all ? i would be interested in any attempts you have made to tame the symptom and if any one adjustment was useless to even try. email or post. thanks, frank

 

This "flaring" at start-up seems to be consistent on other ECMs. It definitely exists on SD 730s also. I am currently going through all the code and analyzing it to see where GM "hardcoded" the "RPM add". There are a LOT of constants that are not defined in the "data portion" of the eprom and tend to be more "hardcoded" in the actual instructions.

The "Minimum Idle Speed when in Gear" is a great example. On the SD 730, it is physically "hardcoded" to 800 rpms with the actual code. My goal is to identify as many of these as possible an develop a "softcode" verson of the $8D so these can easily modified with a Bin Editor like TunerCat.

 

hardcode? is that some kind of data that cant be "deciphered" enough to allow a program like tc to modify it? is there much of that kind of data within a chip for like a 730 ecm? how do you know its there? is it something that takes up "space" on the prom and you can see its there but cannot find the exact relationship it maintains with the rest of the data instructions? if it gets "figured out" how will you know that you were successful? oy- enough questions if you want to answer even one, thats appreciated. got an uphill here to grasp some basics. any piece of knowledge picked up here, may help it fit together down the line.

 

I was wondering the same thing about the idle in gear rpm. My car also sits at exactly 800rpm no matter what my fuel, IAC vs temp, or timing is set at. It seems to just find 800rpm and stay there. When it's cold out and I only have a few minutes to warm up the car the idle is sometimes still at ~1200rpm when I put the car into gear, it drops right down the 800 and the IAC seems to keep it there. Then when it's warm out and my idle might be 600-700 and I put it into gear the idle dips to maybe 500 and then in a blink the IAC opens for a steady 800rpm. I wonder if my ecm has that constant in the eprom or on the board, gonna have to dig through the disassembly again .

 

Is it possible that a worn throttle shaft (?) in the throttle body is leaking and causing higher revs? My car has this problem i.e. the bushings are worn and the throttle plates sometimes seem to stick open "just a bit", so the revs stay a little high. Mine is a 5-speed car so it's not an issue, but it would be a hassle with an automatic.

GreaseApe has it right with the carburetor equivalent. The dashpot allowed a bit of air to keep flowing so that the overrich mixture produced on overrun wouldn't escape unburned. Some carbs also used a solenoid that completely closed the throttle so the car wouldn't diesel after shutting it off. Ah, the bad-old-days of emission tuning...

 

I have seen quite a few TPI units with this problem.

Works nice for engines with big cam, high idle, and carb.

 

hardcoding is a programming term for when something is written so that it can't be changed easily.

In the bin files, there are tables, flags, etc. that you can change with tunercat. This is good because you don't want to search through the code for every time you change the injector size. The ECM says hey, I need to know the injector size, I look at this position.

I haven't looked at the code, but it seems like there are specific areas where the ECM does a 'add 200rpm' instruction... this is hardcoded because the 200rpm value isn't set anywhere in the tables.

Clear as mud?

 

is the code in the prom only?-i guess it couldnt be, because the car will fire up and "run" w/o the prom. ok-so the engineers wanted certain parameters difficult or impossible to change, impossible meaning that the skill level (and)or determination required to figure the difficult parts would not be present in most individuals? could it be said that the difficult parts to figure out are the ones "hardcoded" into the system? why are some easy to manipulate and others not so? is the stuff we do programming the chip actually the easy part and the difficult part is determining how and what causes the ecm to compute its decisions "independently"? of the chip? is it similar to the 870 ecm where there is a separate mask rom chip that is there to help the ecm do its thing,and i think, to throw some curveballs to someone trying to perform brain surgery on it? who works at motorola? again just wanting to grasp some basics here, any answer is appreciated.

 

Since McDonald's workers can program a PROM, I would say that most (definitely not all) of us do the easy part. No, I am not saying where I work.......
J

 

good-the answer man-heres another-how come i cant get 3 sausage mcmuffins with egg, 2 hash browns and a 42 oz. coke and have it add up the same for even 2 days in a row? edit- ah-ha the answer was just explained to me and darnit, im too obtuse to pick up on the wisdom-its cuz they are too busy burning their proms, right?.

 

Close. Where I live, jobs are scarce and it's basically all that is available for many college students (Starbucks if they're lucky). Kind of intimidating for many of us older guys to order a burger from a person that often has more education that ourselves. "I'll have a Big Mac, side of fries and a PhD."

 

well then-the prom burning that they are doing in their "free time" should not be allowed to interfere with the attention required to properly manipulate a cash register. or if its the old-cant walk, breathe and chew gum at the same time, kind of 90's gen X guy (or gal) we are discussing here. the individual has no business taking on more tasks until the 3 mentioned above are handled. or spit out the gum. ok,ok, ok-stand still too. then tommorow im asking for my food and a bin file to go with ketchup.

 

GM originally stared out with modules or packets of bits of code, you want a VE table, here's the code, timing for a distributor, OK, DIS, it's over here. Now they have a calibraion with all the perameters they think they need.

So they hit the chassis dyno.
Tweak tweak tweak
OK, it runs, now run an EPA cycle
again
tweak tweak tweak tweak

OK, off to the real world OK, we can drive the car here in Michigan, so off to death valley,
Ooops
Car don't run in 110dF temps
tweak tweak tweak
OK runs here

Off to the great white north.
Hmm no start.
Again tweak tweak tweak.

Back to running EPA cycle. oops massive problem

Back to Death Valley
Canadia

EPA cycle

Tweaking not only means calibration changes but also code changes, the guys driving the cars would call into home and the software guys would guess over the phone to cure the problem.

The code in the C3 and P4 ecms is incrediably old. ie predates the Cross Fire Production.

The P66s are a whole new game, and the latest flash are actually pretty much pure (none code tweaked in developement).

From what I've heard the 2003 Caddie Sports Car code is 1/2 magic..

 

then the c3 and p4 and myself have found our common denominator. hey-right on- i just got some knowledge-(actually the real motivation to be here. if ya told me a year ago i would be typing like i do these days, a lightning quick pace, up to 5 words a minute, "haha" i would have said with my hands on my hips and a tilt of an eyebrow. but you'd be right and i'd be wrong) the chip is the calibration-(memcal-been saying it for years) doh so the ecm is the the code within the aluminum box that the prom influences to behave the way its needed? and that need is dictated by the driveability (and emission) constraints imposed upon the intended usage, for whatever reason? ok dont take this the wrong way- its the only way i can describe it-the prom reprogramming is generally the "easy" part and the "hard" part is the inner workings, the code, in the ecm? things go on in there which must be understood to fully gain control "full tunability"of all possible parameters? am i kind of close? why is it so difficult? i dont mean that any way except the way its written. its an actual "code" that is in there which is so good that its way impossible to break-like where some symbol(byte?) actually means something else? or performs a task that is not what is expected? what computer intro book needs to be referred to to grasp the concept better? t.i.a. fer the help

 

I asked tunercat about the throttle follower for the lt1, and they sent me a defintion file with it included I will reduce that a little and see how I like it, I don't want to do away with it completely, but it is ANNOYING the way it is now. Thanks