Guys,

For anyone fighting with their ECM to get a nice idle, I had great success doing the following:

Set the idle requested rpm to 600 rpm

Set the idle stop screw to give me 650 rpm

Change the spark advance vs idle speed correction to 0

Change the spark retard vs idle speed correction to 0


This gives me consistent rpm and a stable spark at all times. I got tired of trying to make the ECM do what I want, so I basically told it "you're fired!" The ECM no longer has any influence on idle speed and it's never been better.

 

usually i find that if i flatten the area surounding the idle VE and idle spark and create a platuea the idle smooths out very nicely. Ive done this with some pretty radical cams so it seems to work very well. Also your idle target of 650 rpm might be to low for it to have sufficent vacum to idle well. maybe some detials on the combo your running could help some of us vetrans help you.

 

How's this work?.

 

My combo is not that radical. The cam has only 212° intake duration and the rest of the combo is in my signature.

I had the idle pretty decent before, but after having read Grumpy's statement about having zero idle steps, this new way is working out perfectly. I'm totally satisfied with the way it's runnning. It idles very nicely at 650 rpm with about 15" vacuum. No help needed here.

 

well if you have a port injected engine this doesnt make much sense. Usaully this zero step trick works best with tbi setups. there is something wrong with the tunning if the engine cant achive the target idle. I dont want you to take that statement the wrong way but i can get motors with cams in the 280 @ 50 range with 106 lda to idle at 750 rpm. SO my advice is to flatten the areas up or down 1 step from where the engine idles on the map and see if that helps. then let the ecm take control of the idle. if you have a great deal of idle vacum fluxuation the ecm will defintely get crazy on you.

 

what raisint the idle will defiantely bring up vacum. the faster the pump turns the more air it draws. usually i add a ton of spark to get it pulling vacum. then ill play with the idle speeds until i find one that seems to work the best with avg vacum. raising the idle also helps to stop some of the self egr and intake reversion thats so prevelant in short runner large plenum engines.

 

I don't think he ever said he can't acheive target idle, he just said that he tried Grumpy's advice and gained a more steady idle.
I usually run with little idle steps - 15 or less. Car idles great either way so I try to keep a little.

 

Each cylinder event is going to generate a given intake tract pulse, changing the speed just changes the frequency at which they happen.

I thought you've said Reversion doesn't really exist...

 

It works equally well with anything using an C3/P4 ecm and an IAC.

 

No i siad reversion from the port to the maf cant be found in any testing ive done. my testing involved 3 lab quality mass air metter and 2 map sensors along with acrylic tubbing and a smoke machine to measure mean pressure across the tubing. Tested it with about 4 different cams and was still un able to produce anything approaching a phenomenon you keep describing but lack any proof to back up. tried lda and intake durations that should have easily created the phenomenon. the shorter the runner the more likely the problem is to occur. But our testing included both for and gm engines with a variety of intake manifolds. from the stealth ram to the minram to the stock tpi to a completely done up edelbrock tpi unit. not to mention the plethora of tpi style mustang intakes.

Ive put my time and effort into proving or disproving your ( Theory) about siad intake reversion and time and time again i come up empty handed. The whole problem with you thoery is that the air mass outside the engine is far greater then the air mass inside the engine. not to mention that at any given rpm the pressure in the atmosphere has to be higher then the presure in the intake ducting or else the engine wont breather. IE if there no vacum there is no air movement.

Like i siad ive done the testing. Un fortunenately for you guys here its the intelctual properyt of the company i used to work for so i can not share it. Sorry.

 

Look folks, I didn't mean for this post to turn into a p!ssing contest. 87_TA is correct, this was merely to state that, having taken Grumpy's advice, I was able to achieve a more stable idle than when I had the ECM in control of it. I didn't say it was unstable beforehand. That's all.

Let's just call it a day and leave it at that.

 

How has your drivability been ULTM8Z?
Is the stumble all gone?

 

Matter of fact it is! Thanks. The misfire too. Turned out that my charcoal cannister vent line to the tank was clogged up. I disconnected it from the tank and blew it out with some carburetor cleaner and compressed air. Worked like a charm. I'm in the process of tuning it now, since I never got the chance with my new cam and heads. It's coming along very nicely.

 

Wow, Great!
Guess that explains why it worsened when you added more A/E .
I imagine that would be about the last thing I would ever check.
Good find and congrats

 

thats exactly what i want to do. how? im using tuner pro and cant figure out an idle request anywhere in there. all i have seen is iac stuff but i dont know what to do. i am using a 7730 type ecm 8d ? i think. speed density. please help if u can. i know you can.

 

tpi shivy, to do what you want to do,
use the procedure here, https://www.thirdgen.org/tpimod2 to set the Idle Air Control. this will set the minimum air, disregard the speed in the article & set your base idle to the speed you want. check the TPS adjustment.

depending on the idle speed you want, you may not need to do this next part.
now open TunerPro & look in "Tables", find "Idle Engine Speed Vs. Temp", now set the speed in there to a little lower number than what you want your motor to idle at. burn a chip & install it. clear the ECM memory.

once your done, warm the motor up & verify you have zero IAC counts & the motor is idling where you want it.

don't pull the speed down at the colder temps too much, or you may have problems with it stalling when cold.

 

ok. this is gonna sound dumb but oh well here goes. how do i verify zero iac counts. and what are they? as you can see im new to this.I guess il tell you that the aplication is on a 79 chevy truck. engine is stock with 1 1/2 headers and 3 inch collectors into dual flowmasters. the fuel press. is set at 42 psi at idle. the cam is also stock. i have 24# injectors. the timing is set at 10 degrees btdc. the problem im having is high idle and surging at idle. this to me is indicative of a vacum leak but i cannot find one anywhere. possibly throttlebody or cam maybe? how about fpr? my fpr is non adjustable. thanx any help is much appreciated.

 

Did you install an O2 sensor? If not, you can still run open loop, just disable the Closed loop by setting the min temperature in the chip.

Oh, is your fuel pressure regulator connected to the intake manifold with a vacuum line? It should be. That would reduce your fuel pressure at idle to about 35, and is the right thing to do. The vacuum reference keeps the fuel pressure "across the injector" at a constant, so that vacuum in the manifold doesn't "suck" more fuel out the injector than it's supposed to.

Also, set your injector constants to 24#.

There's an "Idle Engine Speed vs Temp" table in $8D. If your XDF doesn't have it, I could email you one that does. Just PM me.

If you can connect to the ALDL connector via an autoprom or other diagnostic cable, you'd be able to "log" your data. Then, you'll see what the engine is doing in real-time. It'll show you the IAC counts as well. If you open the throttle screw some at key off, key on, start, then check your IAC counts when fully warm, you'll see that opening the throttle screw will reduce your necessary IAC counts to maintain the "commanded" idle speed.

 

more info is always a good thing.

check every thing like RednGold said.
the injector constant & fuel pressure have to be right before making any other changes. otherwise you'll never get it to run right.
where you at right now, your running rich which will cause problems even in open loop.

 

thanx guys. i have set it to run in open loop and the surging reduced but still there. i dont have a aldl cable yet but i will get one from moates. also redngold you mentiond me fuel pressure should go down to 35lbs but i get 42lbs with vacum connected or not! im gonna go ahead and get a new fpr and go from there. like you guys said find this gremlin first. oh yea the 02 is a univ 3 wire. and all other sensors are less than a month old. the whole install is less than a month old.

 

If your vac is staying at 42 regardless of whether the FPR vac line is connected then there is something wrong. Either a bad FPR or the vac line is broken, cracked, plugged, etc.

 

im waiting on a fpr non of my local parts stores had an adjustable one. i checked all my hoses for leaks (vacum) and all seem good. i'll let everyone know how it goes with a new fpr.

 

Where do you have the FPR vac line connected? You should hear the vac hiss when you pull the line off the FPR