Pablo

iTrader: (1)

this might sound like a dumb question, but what does the IAC do at WOT? does it go full shut or does it open?
It closes right? just making sure here

Pablo

iTrader: (1)

did some reading

and some analysis of some diacom runs and no it doesnt close

very interesting stuff, the IAC is alot more important than we give it credit for, for us guys with big cams and slightly choppy idles modifying the iac pintle can be of extreme benefit, im gonna mess with mine now

Pablo

iTrader: (1)

ok i chucked the pintle into a drill and filed down the ledge from the first to the second step quite a bit (on my spare iac) then reset minimum idle, the reset the ecm
started it and it was a little hard to start it was idling real low had to tap the gas a few times go get it going
but once i let it idle, and drove around a bit the difference was huge in terms of how smooth the car was at real light throttle and idling and i think i also picked up some airflow on the top end because it seems to be leaning out a bit more
i stopped and tried to restart and it was hard to start again in terms of it idling real low, i think this spare iac motor i used is no good, getting slow or something, im gonna revert back to the old one and see how it is

FastBroker

I think you can adjust (on the PROM) the value that the IAC will "stay" at under normal non-idle driving conditions. On TunerCat you can, anyway. [IAC steps vs Engine Coolant]??? MOst are set for 25 at operating temp. IF you don't runn VSS, you may have some serious problems w/IAC position at driving speeds, including WOT. I think the ECU will move IAC up (about 80-100) if no vss signal found and engine rpms go off idle speed control. ECU does this to keep motor from stalling when you quickly drop off the throttle (ie, dashpot) and w/no VSS, ECU basically thinks engine is freewheeling in neutral, even though in a gear...

Pablo

iTrader: (1)

Hmm i noticed that, i also noticed that in the ecm constants theres an IAC steps in park (at 160 on mine im issuming this is what revs your motor on start up) and IAC park or neutral offset. Just to experiment i moved the IAC park or neutral offset down to 0 (it was like at 13) because i guessed that was always added at idle (my car was idling high after the IAC mod and yes i did reset minum idle)
The thing i dont get is that you put in the desired idle speed.. yet this (iac steps) seems like yet another parameter that affects idle speed
im guessing that these are the base numbers the computer uses to adjust idle and it would also seem that the lower the IAC steps the better.

I think im gonna reset minimum idle to within 50 rpm of where i want it to be with the iac hooked up, and take off 20 steps across the board on the IAC steps vs coolant so more of the air is going through the tb than past it through that vacuum leak of an IAC, ill let you know how it goes

FastBroker

That IAC Park position is the position that the IAC will "park" at when you turn off the motor... usually, wide open at 160(?)

P J Moran

I found this old thread with a search...

This might explain my problem. Wanting a higher idle speed, I went through "the procedure" and using the screw I set minimum air at 750rpm. I reset the TPS, etc. But now, the car wants to idle way too fast, but does eventually slow itself down after a couple of seconds or so.

Just having gotten my software, I have found that I can set both the minimum idle speeds and the "park" position. I have concluded that with my minimum air set so high, the park position for the IAC is now too high and is holding the idle up until it realizes it needs to close down some.

Should I just reduce the park position (it's 80 in my BIN) to get it closer, or should I go back through "the procedure" and set my minimum air closer to the 550 mark and use the prom to raise the idle (and leave the park position alone)? I don't have a scan tool, but I suspect that because my minimum air is set higher than the ECM wants to idle, the IAC is closing all the way down from its park position.

I'm really enjoying this PROM stuff! If there was only a way to bump the idle speed when the A/C compressor kicks in...

------------------
'87 IROC 5.7l TPI - original owner!

GregWestphal

iTrader: (1)

I thought the IAC park position is only used for when the car is started up, as in that's where the IAC is parked upon shut-down and starts from there.

As far as bumping up the idle speed when the A/C is turned on, it's there, although it might not be in all of the tuner programs. I know GMEPro has it...

------------------
Greg Westphal
'87 IROC 305TPI/A4

Grim Reaper

Greg is correct, you can control your "desired idle" within the eprom. You can set the idle based on specific coolant temperatures, you can control the amount of additional rpm when in Park/Neutral and when the A/C is on.

If found that reducing my additional rpm when in Park/Neutral from +100 rpm to +50 rpm, eliminated the "surge" in my transmission (which made a "clunk" sound) caused by the additional rpm when moving my gear selector from Park to Reverse, Park to Drive, Drive to Reverse and Reverse to Drive.

P J Moran

OK, my table is labeled "Warm IAC park (steps)". To me, that sounds like the position (in counts) where the IAC "parks" before making adjustments. It's its home base. Note that it's labeled in counts, not RPM. This definition makes sense when you look at the change in behavior after resetting minimum air. When I approach a red light and let off the gas to coast down, the engine won't slow down right away and I have to use the brake more. The idle stays up, too, for a couple of seconds before finally easing on down to the proper value.

You might have a different table for your car that sorta sounds like the one I'm looking at, but it really isn't. It also sounds like something I would like to work with to eliminate that "clunk" you refer to.

TunerCat has a table for the idle RPM -- true. But there is no table for additional RPM when in Park or Neutral, per se, nor is there any for RPM bump with A/C on. Those tables must be unique to your car and/or tuning software. Mine's a lowly $32B



------------------
'87 IROC 5.7l TPI - original owner!

Grim Reaper

Use the IDLE RPM table, that is the one that will determine you idle speed based on coolant if it is similar to the one I have on my 8D.

The A/C rpm add, and Park/Neutral add were on the "Constants Table" for my 8D. Take a look there, I think it is the second table just below the "Switches".

Don't go bashing your "lowly" 32B. I strongly believe those tables and constants are there within the eprom. The problem is that they may not be defined for the 32B.TDF from TunerCat. You gotta get the hack for the 32B. With that, you can locate where the table or constant REALLY is and then make a corresponding change using TDF Editor (also from TunerCat). It is FREE for 30 days (though I have now bought it). I have already added a few constants and tables based on information I found in my 8D hack.

I am discovering that the TDF files are only the "tip" of the iceberg as to what is REALLY in the ecm. For most beginners, the tables by themselves are quite intimidating. But after awhile, you begin to crave "more things to play with". That is when the "hack" and the TDF Editor becomes useful.

Go here http://www.geocities.com/ecmguy.geo/tuning/do_tune.html and there is a sample hack for the 32. You can also make a post and I am sure someone has a specific hack for the 32B or tell you the differences between the 32 and 32B.

Grumpy

Off idle the IAC acts as a dash pot.
On a 87 350 I tried several pintles and lost several MPH by using different ones, the OEM was best
The steps **kinda** represent 25 rpm per step. That is on a GM Truck TBI, and running a Stepper motor controller to move the IAC around, again your results may vary

The park posistion is for helping chunks of carbon fall off as far as I can tell. My park is a 90 count down from 125.

Fooling with the IAC has alot to do with overrun, and sudden transistions. Not enough and you can get to stalling. Get everything else right and the play with it, is my advise,

P J Moran

Some new developments...

Yesterday during lunch, I installed an EPROM with the minimum idle set at 750rpm. Last night I went through "the procedure" to reset minimum air (car at operating temperature). Terminals jumpered, ignition on, wait 30 seconds. When I grasped the connector on the IAC valve, I felt a rapid ticking. I gave it some time to stop (thinking it hadn't closed yet), but it continued. It stopped once I disconnected it. Should it do this? I assumed that once the stepper had the pintle all the way in, it would stop.

I hooked up an "engine analyzer" with a presumably accurate tach. I started the car, set the parking brake, and put it into Drive. I backed the screw out slightly to set (reduce) minimum air to a wobbly 600rpm. Shut off engine, reconnect IAC, reset TPS, clear codes, and restart car.

It idles at nearly 900rpm! My dash tach reads closer to 800rpm. In neutral, it is over 1000rpm! Why is this? Does the ECM think it's running slower than it actually is? Are both of my tachs wrong?

------------------
'87 IROC 5.7l TPI - original owner!

Grumpy

It will just hammer away as long as yu have it set to. That will kill the rachet/paw inside of it. If you want to see one at world by a Stepper motor expeimenters kit and slow it way down, the one I got drives an IAC just fine. Also handy for releashing the pintle and reinstalling
Relly no reason for custom ones, they are a pain to get right BTDT, and generally you'll lose a couple MPH
On a TBI like yous your kinda limited on the dash pot cause the extra air is used.

Grumpy

You've gottne the mechanical adjusstment wrong, or screwy numbers in the IAC stuff, and you may have triggered the AS. Anti-stall

P J Moran

Upon re-reading my post, It looks like I might be confusing matters. There are two problems I am trying to address:
1) The IAC won't stop "ticking" until I disconnect it. This seems wrong - maybe it's not. Perhaps it keeps on ticking (trying to close, although it's already closed) as long as I am in diagnostic mode.
2) The tach issue. Minimum air at 600rpm - EPROM at 750rpm - idle at over 900rpm! Factory tach says 900, engine analyzer tach says closer to 1000rpm! Is it really idling at 750 and both of my tachs read wrong, or is the ECM misreading the rpm, or is it bumping them up for some unknown reason?

------------------
'87 IROC 5.7l TPI - original owner!

Brent

iTrader: (1)

I have observed the same "clicking" when setting minimum air. I believe it is normal. The purpose of diagnostic mode in this case is to run the IAC completely shut. Once the pintle seats, the motor ratchets giving you the sound. I don't believe the IAC should click during normal operation.

When raising your idle did you increase the minmum air speed by the same number of RPMS as you increased the idle in the prom? I don't know if this is the answer but am just curious.

Grumpy

As lond as your telling it to extend it will to try and extend.
Might be in stall saver.

You have the right netres?

P J Moran

Brent,
I bumped the minimum air idle from 400-450 to 600. I bumped EPROM idle speed from 550 to 750. I will have to proceed under the assumption that the IAC is supposed to ratched like that and nothing's wrong. I plan to cut my IAC park position from its current setting of 80 counts and see if that helps.

Grumpy,
Sorry to pick, but I usually can interpret your typo's. What are netres?

Thanks, guys.

------------------
'87 IROC 5.7l TPI - original owner!

Blade

I believe he's talking abou the resistor network on your calpack. You know "the stuff" soldered in next to the actual EPROM. That's what the ECM reads when the EPROM goes bad and it has to go into "limp-home" mode.

------------------
92 Z28 L98 350
------------------
Ported stock heads, XR270HR-10 cam, TES headers, Crane AFPR, Flowmaster catback, MSD ignition components, #24 SVO injectors, 1LE aluminum driveshaft.
Best ET 13.3@107 mph

Click here to see my car at Truspeed.org
Check out Truspeed
Check out the Bin Archive

Grumpy

Not a typo, if you use the correct GM terms, it's short for Network Resistor.

P J Moran

My apologies, Grumpy. My ignorance shines brightly, sometimes.

You could be right, though. I am using the carrier that came with my ADS chip. However, I have run it for years without this problem. I have installed a few chips on it too, recently, without incident. It is only after I set minimum air to 600-650 that my idle problem started.

Last night, I closed the IAC valve and disconnected it. I drove it around that way to see how it behaved. Except for the uncomfortably low and rough idle, I like the way the car acted. After cool down, the car wouldn't idle without a little foot-feed, though. I'm convinced there's something wrong with the IAC system (not broke, just wrong settings). I don't think the ECM is ever completely closing the valve (or is extremely reluctant to do so). I will cut the park position from 80 to 40 and see what that does.

------------------
'87 IROC 5.7l TPI - original owner!

GregWestphal

iTrader: (1)

Quick question: What is your IAC motor count in drive with the engine warmed up? After changing my idle speed from the stock setting and reading numerous discussions on this board and the GM-ECM list about what the IAC count should be at idle, I haven't used the minimum idle air procedures, just looked at the IAC count. At first, it was around 80 or so, which caused the IAC motor to max out at 160 when the engine was cold and trying to bring the idle speed up to what the computer was requesting. I opened up the TB blades a little at a time until I brought my IAC count down to around 30. The engine behaves wonderfully now, just like it should.

------------------
Greg Westphal
'87 IROC 305TPI/A4

P J Moran

I haven't a clue I have managed to get this far without a "scan tool". I really hate to spend that kind of money on a tool, but It looks like I might have to, to get any farther on this.

What you're reporting is consistent with what I'm seeing. ALL I DID WAS INCREASE MINIMUM AIR. I think the IAC's "home base" is now too high and it has to move farther to achieve the desired RPM's. I think that's why it takes so long for the idle speed to back down. That doesn't explain why the idle speed never makes it all the way down to the ECM setting, though. The factory park position (warmed up) is 80 counts; I will reduce all the values in the table by 40. I'll try it out tomorrow and report the results.



------------------
'87 IROC 5.7l TPI - original owner!

GregWestphal

iTrader: (1)

Yep, a scan tool is a necessity to be able to look at these particular kinds of things. They're well worth the investment though...

The park position has absolutely nothing to do with the idle speed once the car is running. All that does is change were the IAC motor is parked once the engine is shut down. This affects how high your engine initially revs the instant it is started, that's it. The warmed-up IAC count is what will be reported on the scan tool and is the lowest (most extended) the IAC motor will go under most normal circumstances.

Why the idle speed doesn't make it down to the ECM-requested speed is because the TB blades are open too far. At that point, I'm sure that the IAC has extended to full open (zero counts), which totally blocks the idle air passage, but that's not enough since too much air is leaking past the TB blades. I think all you have to do is decrease the minimum idle air setting (turn the screw on the TB counter-clockwise to close the TB blades) and that should solve your problem. The only other thing I can think of is that you might have a vacuum leak, which would need to be fixed first before trying to get your idle speed lower. HTH...

------------------
Greg Westphal
'87 IROC 305TPI/A4

P J Moran

Not buyin' it Greg. If that were true, driving with the IAC disconnected wouldn't have worked like it did. Remember, I put the car in diagnostic mode to close the valve, then disconnected it. I drove the car with the valve closed and disconnected so it couldn't open. The idle came down like it should. Once I reconnected it (after shutdown), the idle went right back where it was (too high). For some yet unknown reason, the valve is closing too slowly and stopping short of the correct position. Either the valve is "wearing out" and not moving as it should, or the ECM is not telling it what I want it to.



------------------
'87 IROC 5.7l TPI - original owner!

P J Moran

Well, it looks like it worked. I ran an EPROM yesterday in which the IAC park values were cut by 40 across the board. That left a minimum value of 40. The engine starts fine and quickly idles down like it should. It idles down coming to a stop on the street, too.

With my understanding of the IAC system, I still don't know why this was necessary. It seems that the ECM should quickly see that the idle is too high and bring it down, regardless of where it started. That function is limited only by the range of air flow permitted by the IAC valve. Shut is shut, and my idle acted right with the valve shut (and disconnected). Oh well, I like it, now, and I guess that's the main thing. Thanks for the help.

------------------
'87 IROC 5.7l TPI - original owner!

Pablo

iTrader: (1)

since i posted this (it was awhile back) i saw some more interesting stuff on this subject, Rob Rauscher wrote an article on iac control and what the 7747 does, im sure the general principals are the same for other ecms
I was having a hell of a time trying to get my idle down.. the car would idle real high even though id set minimum idle lower and lower.. the iac was obviously going berzerk

I ended up i believe slightly slowing down the IAC extend and retract response time (cant remember exactly) and the BIG difference was in removing a whole load of steps from IAC steps vs map on restart? i think thats the table.. anyways with a big cam you end up getting into that table since i think it starts at 60 kpa. Now my car will hold the desired idle speed.. give or take a few rpms

Id really like to get the cold idle fixed though, its absolutley attrocious... it sorta lopes around up and down until the puter finally just gets fed up and sticks me at 900 rpm... it comes down as the car warms up though and i do a bit of driving
once the car is warm the idle is great, for the combination anyways, and another complaint is that the car seems to surge at low rpm, low speed,(round 1000) throttle input.. i sorta have to commit myself to give it a substantial amount of gas, if not, and i just lay my foot on the pedal and just give it a little it will sorta jerk back and forth like a bucking bronco.. any ideas on this?

btw i went back to the standard GM pintle when i gained access to the 7747 iac control tables

leirch

Pablo,
Did you ever figure out what was up with that rough open loop idle? Mine does the same thing. And the bucking is the same around those RPMS too.

Thanks,
Brendan


PS. Yea your wondering, where did this post come from?

------------------
1987 IROC-Z L98,SuperRam,EB 6085's,LPE 219/219 Roller, Crane 1.6RR, EB TPI Base, 58mm TB, ADS 24#, AFPR, K&N, EB TES, Catco Cat, 3" Borla Cat-Back, Accel cap,rotor,distro/other crap, MSD 6AL, MSD Blaster 3, Aluminum DS, 94 Disk Rear, Adjustable Valve, Precision 3.73 Gears, Sub-Frame Connectors, Hotchkis Lower Control Arms, KYB Shocks/Struts, Suspension Techniques Lowering Springs, Polyurethan Bushings all over the place, Moog Upper/Lower Ball joints and Tie Rods ends/Idler Arm,

To see the ROC, Check out the webpage Here

Brent

iTrader: (1)

I think Pablo is at boot camp presently.