DVUSz06

02 z06 with btr stage 2 cam, arh longtubes, stock injectors, air box, and car was dyno tuned. 2000 miles on mods. And NO codes logged.
Having an idle issue only when I turn the ac on at idle. The engine will stall, if I'm driving down the road and turn it on it used to stall when I would come to a stop, took it back to tuner and he corrected that, but it still stalls if idling and turn AC on when I first pull out of garage or come out of resturant and turn AC on after meal.
Is this in the tune or is there a vacuum issue or something else going on.
Other wise car runs great, and yes I know I asked this with another question in tech but got no replies from any knowledgeable tuners. I thought I read somewhere that idle with AC on has a different set of parameters that can be adjusted seperate from idle without AC on. Opinions please, I'm going to contact my tuner but would liked to be armed with some knowledge on this situation before I go back.
Thanks all.
Larry

Blue-Z

Sounds like a tune issue. Either the base idle airflow is too low or the ac torque needs to be increased. There are a lot of parameters and things to change for idle, but if it idles ok with ac off, I would think bumping the ac torque would fix it, hard to say without seeing a tune or log.

jglassmaker

On a hot day I would absolutely use the AC, I spend a few hours in HP Tuners getting this kind of thing fixed. I am running a Texas Speed MS4 so AC would nearly kill my car, now you can't tell at all when it engages/disengages.

Here is a screen grab of my tables, they are all in Torque Management -> Engine -> AC Torque. Note a few of these tables you subtract instead of add.

DVUSz06

Thanks guys for confirmation on the AC torque tables, Hopefully my tuner can adjust in there and keep me running cool even when it's 90* outside.
Larry

jglassmaker

Any half decent tuner should be able to do this, point him to my post about which tables if its been a long time for them.

I am not a professional tuner and was able to fix my AC issue in less then 2 hours once I found a guide about which tables to adjust.

tblu92

Absolutely a tuning issue----However realize that when you add a cam you change the vacuum signal that the ECM uses to add air and fuel at idle--Especially when turning on the A/C the engine is under MORE load and the vacuum signal changes----So the stock parameters will not work--------
Don't sell your tuner short--This is basically a trial and error process and may take several attempts to get it "just right" After making changes to idle airflow it does NOT happen immediately as the ECM has to "learn out" the corrected added airflow--So you would need to drive the car at least 50-75 miles using the A/C for the idle airflow tale to settle down-------If you add too much you'll get a hanging idle which can be dangerous as the throttle wan won't idle down ---and if it's auto trans the high idle will make it a bitch to hold at a stop light--

jglassmaker

Just want to share some tuning knowledge...
The idle airflow table or base running airflow is based on ECT, not vacuum - or rather the MAP sensor. The VE table is referenced during open loop and sudden throttle changes, but otherwise the MAF is used to determine fueling even at idle. The MAF is technically affected by vacuum but it is not the same sensor.

Either way these tables should not be touched if already dialed in - they absolutely should not be touched when accounting for AC or accessory load, there are specific tables for these. So driving around and letting the fuel trims adjust won't make a difference since these again are for the base tune.

Any tuner who dares charge someone should know the methods used to disable the computer learning so that they can dial in tables without waiting and making the customer return multiple times just to get the initial tune dialed it pretty well.

Not trying to be a d*ck or anything - just want to clarify and share well documented tuning knowledge that we all should be aware of when dealing with tunes.

DVUSz06

Thanks for the information guys, taking my car and dropping it off at tuner on Monday, they said they want to check AC system to make sure there isn't something going on with compressor. Now I explained that the AC system worked perfect before my cam install and tune. But I have had issues with idle only in AC mode ever since tune. I also had it back once for idle issues and it was made better but still will stall on me in certain situations but not all the time. It hunts for idle everytime AC is turned on but doesn't always stall. I told them they can have car all week just so it gets corrected.
Thanks again guys
Larry

DVUSz06

They will have a hard time getting me convinced that it's an AC compressor issue. One of the forum members that does tuning via internet with data logging and such, would they be able to work on that area if I need to go that way?
Larry

schpenxel

I'd touch base with Pat G and see if he'll check it out remotely

I still think it's in the AC idle airflow settings

DVUSz06

Pick my car up from the tuner today, when I got there he said he made a couple small adjustments, but I still wasn't comfortable with what he did so I asked if he adjusted any the tables in AC torque. When I talked about the tables jglassmaker had showed me he asked to see them. Thanks jglassmaker and hope you don't mind but we used your numbers. Went for a drive and all was ok but the truth will be told on the first teally hot day. It seems that mild temps are not as much of problem but when temps puss 90* is when it seems to be worst.
But I feel better now, hopefully we are headed in right direction.
Again Thanks jglassmaker

jglassmaker

My pleasure

tblu92

Well I disagree---Whenever changing the incoming airflow you need to make an adjustment to correct your LTFT fuel trims so the ECM is NOT adding additional fuel at P/T--Ideally you would want your LTFT fuel trims to be slightly negative or "0" Otherwise even at start up your ECM will be adding fuel even at OL as that % is stored and used at start up And if you have a positive fuel trims "just before going to WOT" that same % will be added to your PE WOT fueling as a lean safety making your WOT pig rich and lazy
The best way to "0" out your fuel trims is with your MAF table --Sure if the LTFT's are above 20% you may elect to adjust your IFR table instead But for smaller LTFT adjustments and data logging you can correct LTFT anomalies much easier and more precisely where needed with your MAF table AND best of all when making LTFT fuel corrections at P/T using the MAF table there is NO LEARNING required as changes here happen immediately

romandian

turn ltfts off and life becomes much easier.

jglassmaker

The best tuners in the business strongly discourage this - its dangerous and doesn't fix the actual problem.

romandian

of course it doesnt fix the problem, but it makes fixig it easier. i see no reason to mess around with the long term trims. whats dangerous about it?

schpenxel

I wouldn't go so far as to say dangerous. I still leave them on personally but I know a lot of others don't

jglassmaker

It can be dangerous because STFT are great when almost always near only 2%+/- but large swings it STFT can cause surging and swing your tune out of commanded AFR. LTFT are used to keep STFT adjustments tamed down and where STFT won't affect PE, LTFT can (depends on PCM). Even if you have everything dialed in perfectly only using STFTs - they can become wildly off again from weather seasons or changing climates.

If you only ever drive in the same area and in the same weather conditions then LTFTs could probably disabled.... I like to drive my car however

tblu92

I agree sometimes with large cams your best option is to simply delete the LTFT fuel corrections----The P/T or closed loop AFR may end up a little off but it will idle and run smoother at P/T---The mileage may suffer a bit but having it run smoother and idle correctly is worth it--

RonSSNova

LTFT have been off in my C5 for years and I haven't been killed yet