Ok guys, so my car (224 cam, full bolt on, A4,tuned) has a terrible time starting when its cold out, better but still not great in summer. Cranks rough, idles messed up until it warms up some needing gas to stay alive in winter. If its summer time fires up much better but have to let the idle setting from 1,500 down to its happy 700 wish range BUT if I put it in drive or reverse before idle settles it just dies/stalls.

SO I did a test, unplugged the IAC fired right up in 40 degree weather (vs crap idle and rough start) and I was able to put it straight into drive and it didn't die.

I have an IAC on order

**A couple questions

Any other ideas on what could cause this besides IAC since unplugging the IAC stopped issues?

Is the relearn process needed for the IAC or just the TPS

Thanks just making sure I am on the right path.

 

Moving this over here to hopefully get more traffic

 

This must be on an Fbody, because the C5s don't have the IAC, IIRC.......

 

Do you have hptuners? Kind of sounds like base running airflow is way off. I THINK that our programs have an IAC park position. If I recall mine is at 150 counts(wide open almost) so unplugging it could leave it parked at wide open. Probably a matter of verifying proper IAC counts at idle(with that small cam it shouldn’t be that big of an issue) and running a Russ k config..however you say it’s been tuned and I assume this is a new issue. The best thing before going down that $100 GM IAC rabbit hole is just try a test of stepping the IAC in and out. My IAC had an intermittent short in one of the 4 wires. It would open and only close half the time it was commanded to. I had continuity from connector to pcm pin every time I checked. I eventually just repinned the 4 wires and rewired it and it’s been working ever since..only sharing cause I now have an extra GM IAC valve. Lmfao

 

Thanks a lot for the reply, this isn't actually too new of a problem. I do not own HPtuners but might look into it just not sure if the learning curve is worth it for one car. It is not the stock engine but still LS1. I had a mail tune from frost for a bit then had a local LS shop tune it and it did this on both tunes. I don't think I have ever tried to start it in winter until this year so I really started to see how much of a problem it is since it is so much worse when cold. It is possible it got worse from the most recent tune not sure.

When you say stepping out the IAC do I need to do this through HPtuners or is it possible to unplug it and unscrew the plunger in different positions and see how it starts?

I like the idea of repining it just because. Not too hard but gets it out of the way.

 

The IACs in this car I don’t think screw or unscrew persé on the plunger end. They use a worm gear setup directly attached to the plunger. So you can move them by heave hoing straight in or out. But I don’t recommend lol.I never broke one doing it but I’m willing to bet they are Easy to break since the whole thing is plastic. A long long time ago, my PO had the car tuned for a small 224/228 cam or something like that and in the receipts he had a slip from frost talking about an IAC adjustment. I will attach instructions for you.
If it’s a brand new issue though I’d suggest as a precursor to any real troubleshooting to do a good cleaning of the iac& throttle body port and while you’re there just spray the maf off with some specialized maf cleaner…and yea you’d need some type of scan tool with bidirectional controls to walk the IAC in and out. Do not turn key on with IAC connected and removed from throttle body. I’m almost sure at initial key on it will try to command ZERO counts(closed all the way) and then will move to IAC park position, but with nothing to stop the IAC it is possible it will over extend the plunger since there is no throttle body to stop it.
Some scanners have IAC controlling as a direct option but any scanner that will let you raise and lower idle speed does the same thing…
the issue I had really is the pcm gets no feedback from the IAC so if there ever is a situation where the pcm sends a step command and the Iac doesn’t follow. It throws the actual IAC position vs what the pcm thinks is the position to be WAY off..either way I’ll attach a copy of the paper sent to my cars previous owner for you to read and chew on. If it’s NEVER been checked then it may be part of your newfound issue. As a side note, i had hptuners(recently upgraded to pro to log wideband) and as an engine diagnostic tool it is much more valuable and capable at the like 400dollar price tag than any couple hundred dollar handheld actron scanner I’ve had.

 

Holy ****, I do not remember seeing that sheet but it does look familiar. That could definitely be part of my issue if not most of it considering I looked past something Frost says is crucial... I would hope my new tune which was not a mail tune they would have checked that though but I am less than thrilled with that shop anyways so who knows. I have cleaned the IAC, throttle body and MAFS. I know the IAC has a plunger t it that if turned on when out of the throttle body it can come all the way out. You are really selling me on HPtuners here! I'm going to be doing a smoke test for vacuum leaks soon just to play it safe too.

There is also an IAC relearn procedure I think or is that only for the TPS where you start the car turn it off and some other voodoo?

Thanks for all this advice its a HUGE help for me to find some decent points to look at. Really appreciate it

 

yes I believe there IS an iac relearn but I’m not 100% certain the procedure anymore. I think idle for 15 minutes in park with e brake on and then drive with e brake. You can look it up on this forums somewhere. Tbh I never noticed a difference in doing it though.

I really do like my hptuners suite. I’ve used it on my own car, a few friends and some domestic vehicles at the shop. It’s VERY good for data logging sensors such as O2 sensors being able to make chart graphs and histograms. now it isn’t a $2k+ scanner like we have at the shop than can do abs and things like that, But for 400bucks it’s well above and beyond what my $300 actron handheld can do and it doubles down being able to modify my f body tune.

My car started like poo like yours and it took a lot of tinkering in some tables to get it just how I like it. Car doesn’t flare when started and settles down nice but it’s a lot of trial and error. If your shop only did a dyno tune and not much street tuning it’s pretty likely they didn’t do much to it…chances are if it drives kind of crummy in areas they probably didn’t spend much time on it. There isn’t much to tuning a maf car. They probably hit the VE table to about 3-4K rpm and then just did a maf curve. not saying they hacked ur tune but that drivability stuff is time consuming. it took me a good bit of seat time to get down. But back to your cold starting issue it’s pretty likely it’s in the tune, especially if it’s been an ongoing issue since the cam swap. I’ve heard frosts mail tunes are pretty damn good for things like a cam only swap. Don’t doubt that dyno shop didn’t just hose you to do a WOT pull or two and kick it back out the door to be honest.

If the throttle body blade is not set right from the start then there is nothing else you can do until that’s set properly because that throws all of the base running airflow tables a little off. If they are close, you’ll get away with it but the proper way would be to get iac to 60 counts hot idle with fans off. Then shut it off and walk away and log a cold start with the Russ k idle air config running and make adjustments to your base running airflow table.

 

Yeah definitely sounds like a worthy investment I am a little more worried about the learning curve of tuning just for one car but as it shows with you helping me, there is help to be had on the forums. I am with you tho and leaning towards the tune. Seeing what the IAC count is vs trial and error would really get this right. No doubt they didn't look into actual drivability. I am around Chicago with a ton of LS shops but a chunk of them you just can't trust with things they can skimp on because they ride their name vs putting in the work on things like tunes.

I will run through throttle screw, vacuum leak check, new IAC(have it anyway). It starts fine with the IAC unplugged tho this all seems to make sense and finally land on the tune. Plus side is on a nice warm summer day fires up fine(ish) so there is that.

 

Yes, there is a learning curve. It’s sharp at first but as soon as you get over the hump it just becomes easier to grasp everything. There are many many great guys on not only this forum but also on HPtuners forums. A really good one from here is chopperdoc. He has YouTube videos as well. Another guy on YouTube is named goatroap garage that does a lot of in depth tutorials. I started off with the base mvpi2 package and I didn’t know a dang thing about it lol. But between other members here,on hptuners and tutorials I’ve learned a lot, I’m now going forced induction and will be tuning my own setup so I’ve come a long way lol. Im very happy I have mine.
If you had hptuners you could simply fix this yourself, record a data log and post it to us for us to look at, etc. if I had to do it all again I’d just have got the pro package from the get go. Being able to log my wideband is amazing how much easier tuning my fueling is and it was shocking how rich my WOT areas were.

 

Chopperdoc has been my go to for the past 48 hours of reading up/watching vids on tuning. Just a very willing to help guy it seems. You are right on the fact its a worthy investment just for the fact I can live data log. I have absolutely been dreading paying another tuner $650 to just push it out the door as fast as possible. HP pro huh, time to read up. I only have an Apple laptop too so from what I gather I will be investing in a windows laptop too.

What kind of numbers are you expecting going FI? Procharge, turbo?

 

Yea it’s just an mvpi2 with the pro features unlocked and the pro link cable. If you don’t have a wideband, there’s no need for it. But WOT tuning should be done with a wideband. It’s just so much safer and honestly way easier to tune with the wideband

And I’m going with a procharger. My car is SBE with a 235/243 NA cam and higher compression prc 225 heads. I’ve got pretty much everything in hand or in order for the pro charger setup except the head unit itself(thanks again to Bob from brute speed) im not hoping for much. I know people have pumped out over 600wheel on the stock bottom. Im hoping to just run around 5-7 PSI and spray it with meth to keep the 11:1 compression ratio happy. It’s not really an if scenario but a when kind of thing on when the little Ls1 ***** a rod out the oil pan lol. I plan on going with a built block in the future from Thompson motorsports and it’s not feasible to even mess with my block when I can buy a vendor shortblock for what I’d have in my motor in time and money pulling it and hauling it around to machine shops...

The old Ls1 has been a very strong motor, been eating 7k rev limiters and near 7k shifts for 30k miles now. Grenaded a 10 bolt and then twisted the housing in 10k miles after I rebuilt it.(it can’t kill the 9” from Midwest chassis though lol) Piston slaps like a **** when cold like usual but just keeps on going strong. It won’t be optimal but should make mid 500s if It can hold it together. But hey, it’ll be fast as hell Atleast once lol.

Also, on the laptop OS side idk if hptuners has programs for the apple, but if I had to I’d hunt eBay on a cheap windows laptop. Also, you can download the hptuners suite to try it out and play in the files. They have I think a Gen 4 Camaro tune file in the tester files that should match what you have. If you plan on ever going further with your car it’s a worthwhile investment IMO

 

Not gonna lie, it’s always cool seeing my name tossed around for good advice. I’ll also be honest that I may have not read every letter of this thread, but I didn’t see anything mentioned about the idle set screw. That thing will drive you ******* insane. It will move sometimes unless you use a jam nut or a little locktite.

Give it a turn or two and see if that clears up the issue. Also, I fully agree in learning how to tune. It’s way cheaper in the end. You’re still on Gen III where it’s easy. Gen V had me back on YouTube and in forums learning how to tune one of those the first time. Like damn. Really GM? Torque is load now? Based on airflow? Okay then. It’s massively different.