Jim85IROC

iTrader: (2)

I did a search and found very little information about setting the minimum air on a manual car. I found 1 thread where vader said to set it at 450rpm in neutral. My problem is that I'm not sure if my car can even sustain that kind of idle without stalling. Tonight I fired it and couldn't get it to idle. For some background, I just converted to a 165 ECM with a harness out of an 87 IROC. The PROM is an ARAP with considerably more conservative timing. I have a brand new holley 52mm throttle body and the idle screw was at its factory setting. I adjusted the IAC previously to .52 volts with the blades closed, around 4.68 at WOT. But... the only way I could get the car to idle was to move the screw out pretty far. I did this just so I could set my timing (I'm at around 5 or 6* base timing currently). The car seems to hold an idle at 750rpm, although it's smoother at 850-1,000. The TPS voltage is .66 volts and my IAC counts seem to be between 130 and 160.

So... I'm assuming that I need to follow the tech article to set my minimum air. 450 rpm? Then when I reset the TPS, I want .5 volts with the blades closed and 4.5-4.75 at WOT, right?

Any help will be appreciated. Thanks.

Ed Maher

Ideally you want to look at it on a scan tool, and find a setting that gives you relatively low IAC counts at idle.

Jim85IROC

iTrader: (2)

Problem is, my iac counts are high right now, and the screw is turned all the way in. I'm going to need a longer screw if I want to get this thing out any farther.

Ed Maher

What kind of cam do you have in it? Might need more timing to get it to idle stronger.

Jim85IROC

iTrader: (2)

I've got a 214/224 duration cam with a 112lsa.

I think I found that my IAC is spent. I had it running today and my IAC counts never moved from 160. I unplugged the IAC and the idle didn't change. It's stuck closed. I bought a new one and installed it but I didn't fire the car yet. We'll see shortly.

Jim85IROC

iTrader: (2)

Well, I put in a new IAC and nothing changed. My counts are still at 160 and the car won't idle unless I open the throttle blades a mile. This would indicate that the IAC obviously isn't the problem, but when I put the ECM into diagnostic mode, I had voltage at all 4 pins of the connector just like it should. That says that the wiring and presumably the ECM is functioning properly. Now I'm confused.

Brent

iTrader: (1)

Didn't you change some other things at the same time you did the 165 swap? If so I'd look at those things.

IIRC you swapped in a new TB. Maybe the passages are blocked.....

Jim85IROC

iTrader: (2)

Yeah, I put a holley 52mm unit on. Brand new. I suppose I could pull it off and see if for some reason if it wasn't machined properly.

Drkhrse89

iTrader: (1)

When I initally bought my car there was a holley tb on my car and the guy told me that it had to be machined to fit. The passages were not the same as the stock throttle body. I am sorry that wasnt more help but I would compare the 2 of them and I bet that there is something not right.

BOTTLEDZ28

iTrader: (9)

I am having this same problem with my car. I just put a new engine in and all new sensors and the car idles at 1500 most of the time. other times it will drop to about 800 at a light. I put a new TPS and IAC in and nothing helped me there. Also, at idle in neutral the car will search for an idle between 1500 and 1900. it wil rev up and down like I have a cam in it. I cant figure it out. If anyone has a clue on where I should look please let me know.
Jim85IROC, if you find the prblem let me know. I will be rechecking my IAC and TPS values for the 1000th time this weekend again.

Jim85IROC

iTrader: (2)

My car doesn't hunt for an idle. It used to when I had the old 870 ECM, but not anymore with the 165. It hunts for just a few seconds if I don't have ample throttle after startup, but then it stablizes and idles very well.... but it's with the throttle blades opened to compensate for the IAC that's closed.

Ed Maher

It could be an issue with the IAC passages not lining up. It would be worth checking.

It also might want more timing at idle, but i told you that already, dunno why you haven't checked that yet either.

Also might be the stock chip is trying to idle you too low for tat cam, but that much should be obvious.

C'mon Jim. All the real dirty and difficult isses you've had to fight with that car, and now you're not checking any of this little easy stuff to make it idle correctly. Maybe you're getting a little burnt out and need to leave it alone for a week or something, cuz it doesn't seem like you're really trying to fix it (i.e. you're hesitating/thinking like this is another expensive or hard problem, rather than playing with what needs to be played with.)

Jim85IROC

iTrader: (2)

Sorry ed.

I'm working the schedule from hell this week. 6:00PM- ???? and it's been too hot to work on the car during the day. Right now I'm bench tuning until I can actually get back and work on it. Today I may have a chance. I don't remember what this chip is set to idle at, but I think it's a little higher than stock. My x-ray said that the desired idle was 750 once it reached temperature. I'd change it, but my copy of GMEPro and my copy of Tunercat either won't install or won't allow me to save bins anymore, so I'm stuck with this chip until I get another copy of one of those.

I really don't want to screw with the timing if I don't have to. The car liked 4-8* of timing with the old computer, so it should like the 6* I'm giving it now. I hate to advance it any more because of those old fuelie heads & my flat top pistons. That's a combination that's just asking to detonate.

But anyway... I'll see if I can get the tb off tonight and verify that the IAC passages are open.

Ed Maher

Like i said, sounds like you're on the burnt out side and need to step away for a couple days. Happens to me all the time, hell, i've been burnt out all summer on my car. I had big plans for it, but so much has been happening that i just can't get into working on her.

I hear you about the timing thing, thats where PROM burning helps. For now, just see what timing does to your idle quality / vacuum. You don't have to permanently leave it set there, but at least you'll know if another 5-10' of timing @ idle cleans it up. Then once your burning set-up is back online, you put that into the chip.

As for the idle speed, 750 shouldn't be too low for that cam, it isn't like it's that big. But it wouldn't be all bad to experiment just to make sure once your set-up again.

As for the IAC passages, we all know how easy the TB is to pull. If you can't get around topulling the TB to check it you're definitely burt out on the car for the time being. How do i know. My car had a bad stalling / wandering idle for 2-3 months. I finally got around to cleaning it as well as cleaning my cap and rotor last week. I too have been that burnt out by the time i left work that even removing 4 bolts right in front of my face was too much a pita. So i feel your pain, but nonetheless, until you check this little stuff, i don't think you're going to find a magic bullet by bumping this post

Jim85IROC

iTrader: (2)

I planned on pulling it tonight, but I spent the WHOLE night trying to get my modem to work. Unsucessfully I might add. I'm getting sick of going to my parents to use the Internet. Tomorrow I've got crap going on... maybe thursday.

Moving into a new apartment and getting stuck on a goofy 2nd shift schedule really eats up your time.

But anyway... I'm going to crap if I find some sort of blockage. The holley TB is brand new and I don't remember noticing any oddities about the IAC passages. The lower housing was thoroughly cleaned and I made a new gasket for it before installing it. I'm going to be real suprised if I pull that off and find something blocked.

Jim85IROC

iTrader: (2)

I pulled the TB. The IAC passages are machined properly and line up perfectly to the passages on the IAC housing. I'm totally stumped. I even checked the TB gasket to make sure that nothing was interfering. It's all kosher. I tested all 4 pins of the IAC connector with the ECM in diagnostic mode and they all check out. So, I'm totally stumped. New IAC, new TB, perfectly clean & open IAC passages, and the sonofabitch isn't doing a damned thing. The IAC is 1/2 open, not totally closed. The impression that I get from reading my Helm manual is that the IAC should return to the fully closed position when the car is turned off. I'm totally lost here.

Brent

iTrader: (1)

That's whack. If you set minimum idle higher than the commanded idle, the IAC *should* run down to 0 counts after the car is warmed up.

I'm thinking maybe the ECM is flaky.

Chrome

carb, carb ,carb...

hehe, just jokin...

anyways, i'm kindal leaning towards ed's idea. sounds like it needs more timing and i think the best routes a custom chip... I think the IAC is a lost cause, i've worked on GM vehicles w/ IAC's and i'm suspected them everytime and /every/ time it turned out NOT to be the IAC.

Ed Maher

Chrome has a point. Like i said i've had a flaky/stalling idle problem for months. Cleaning the IAC didn;t do anything for me. Cleaning the contacts in my distributor cap did.

There's an old adage for carned cars that is equally true for any engine. 99% of carb problems are in the ignition. It's easy for dumb ignition issues to make it seem like your fuel or air supply is screwed up.

If i were you i'd crank the dizzy up with a vacuum guage on it while idling warmed up and in closed loop and look for best vacuum.

jmd

iTrader: (4)

Just a thought to throw out there, but what are the differences in the TB gaskets (that come w/ a FelPro intake set) for? One looks like "goggles" and the other has the 2 TB bores + a triangle. Would the wrong gasket w/ Jims Holley TB cause his issues?

Chrome

ya know just another thought, might check your injectors... ???

SATURN5

Have you by chance put the original TB back on? Did the IAC still act up? or did it "clear" up? Try and narrow things down. If the car ran good with the orignal TB then I don't see changing TB's would effect the timing...not at idle. I do remember a thread a whilest back regarding idle timing with the HOT cam. Seems they were running quite a bit of "chip" timing at idle/off idle. cheers, Bob

Jim85IROC

iTrader: (2)

I may try the stock throttle body tomorrow. I don't think it's my injectors but I suppose anything is possible. The injectors are basically new and just removing them and reinstalling them shouldn't cause problems.

The holley TB does have different shaped IAC passages, but nothing that should inhibit flow. The section of the lower housing where the IAC seats is still the most restrictive portion of the flow path. I doublechecked the gasket and it does not cause any blockage.

I wish I ran the x-ray on the car right before I started these mods. I think my IAC counts were high back then too, but I can't remember.

Beast5spdGTA

Don't count out the MAF, I hate those things, hard to diagnose a problem with them

Jim85IROC

iTrader: (2)

The auto x-ray is showing 8g/s on the MAF at idle. No indications at all that the MAF is at fault.

irocnroll89

iTrader: (4)

just to keep this up top, i too have an intermittent idle problem. A new IAC, and a well adjusted TPS, have have done nothing. The chip is custom, and now i am down to either a vaccum leak , or a sticking TPS rod.
Also If this helps, when the car does "stick" at a high idle, i can get out, pop the hood, and push the throttle blades closed the rest of the way. I feel a click, and then the idle goes down. Many in my car club TEAM NW F-BODY, think it 's a sticky throttle cable though it too does not stick. Lastly i know i has nothing to do witht the cruise control, disconnected.
Wow , hope some can fix this for one and all, and any thing i find i will share promptly.
SHAGGY

Ed Maher

Not trying to insult you here, but you have checked basic tune-up stuff right? Like i said in a post above, i was bothered by a really bad intermittent low idle / stall for a couple months. Finally got off my lazy *** and cleaned teh IAC and nothing changed. Pulled the distributor cap just on a whim, and cleaned it up with a wire brush. Even though it wasn't horrendously corroded (it's under a year old), it was apparently the problem because everything has been *perfect* since. I don't know how a slightly crusty cap could cause an intermittent problem, but it did

I'm just rementioning it, because i know once we get to the stage of burning PROMs and understanding all the little nuances of how the computer works, we tend to ignore the old 'basics' that we would have checked first thing in the old days.

irocnroll89

iTrader: (4)

I will check after i sleep a few.
I am also going to try to splice the old auto tranny wires together and see if the computer can sense, a neutral/park condition.
later, shaggy

Jim85IROC

iTrader: (2)

Tonight I had time to throw the stock throttle body back on. I threw it on and the car started right up and idled. I looked at the IAC counts and they were pegged at 160, just like before. After it warmed up to about 200* the counts came down to 34 at idle. I don't understand. The holley TB had perfectly clear IAC passages and should have worked just fine. I'm going to throw the holley back on on thursday or friday and screw with it some more. This has me even more confused than before.

Are the IAC counts supposed to be pegged until the car warms up? If so... then shouldn't both TBs behave the same assuming they are adjusted properly? The idle screw on the stock one is almost backed out completely... on the Holley it's turned in as far as it'll go.

I'm as confused as ever.

Jim85IROC

iTrader: (2)

oh yeah... not only was the IAC count pegged at 160 while the car was warming up, but unplugging the IAC made absolutely no difference in the idle. I can't imagine that the IAC only opens once the car is at operating temp.

irocnroll89

iTrader: (4)

well, i have found the problem , with mine, is something is holding my throttle blades open, intermittently.
I know it is something mechanical too. THE only other thing it could be is the wrong T/B gasket not porting air correctly. My IAC is functioning fine according to my X-RAY. The blades are either binding, or air is not being ported right. They stay open only a 1/16" or so, it is not consistent and i can push lever back to the stop screw and it goes right down to 700rpm. SOOOOOOOOO i may need to gut or replace my T/B.
DAMN!!!!!
Shaggy

Jim85IROC

iTrader: (2)

Yeah, my stock TB is doing the same thing. I backed the idle screw out a little but the blades don't want to retract all the way. Might be time to take some fine sandpaper to the throttle bores. Carb cleaner apparently didn't do enough... although I'm really hoping to get the new holley working, otherwise I'm going to wind up with a dead sexy billet aluminum door stop.

irocnroll89

iTrader: (4)

i am going to pull mine back off and do some sand, and alos look at getting anoother gasket. I KNOW there are "2" different T/B gaskets. Whe i got my complete intake set, it had to different gaskets. Well for awhile i used the one that look like the one that was original. Then after it wore out i used the other one even though the out line was ALOT different. Trying to be cheap , may have been my demise!!!!
BOY IT SURE SUCKS ROLLING AROUND TOWN IDLING AT 2500 RPM
good news is the HOOkER cat-back is still sound kick-***!!!
shaggy