1999 Trans am intermittent high idle with AC on

[trocc4]

Hi, have a problem with a 1999 Trans Am that seems to increase idle intermittently when the air condition is turned on. Had the vehicle serviced by a speed shop who were utterly incompetent and couldn't resolve the issue. Did a comparison on a base idle and from what i understand most of the values are zeroed out concerning the AC. This is an area I need some help with the car runs great untiL you turn on the AC. I have VCM Editor file from the car I'm sure most of you are more experienced then I am. Thanks

[blindsquirrel]

https://forum.hptuners.com/showthrea...og-amp-cfg-too

[RDF1]

Post tune and a datalog of the issue..

[trocc4]

Here is the file, not sure what you mean by a data log of the issue. Its a 1999 Trans Am that has an intermittent idle issue when the AC is turned on the idle increases from 700rpm to over 1000rpms I have attached Editor and scanner files .
Appreciate any help

[gtstorey]

Data log is the “scanner” file.

[HATEHPTUNERS]

Start logging IAC counts, and also ALL air channels.. You need to know if the PCM is commanding more air through any of the channels at A/C turn on... Then you can figure out how to address the problem. You can see that when the A/C comes on and the idle goes UP, that the PCM is pulling timing trying to get the idle speed back down.. WHY is it going up? That's the question.. Start monitoring more channels and hopefully you can drill down on the problem. You can also compare your settings in Hp Tuners/Engine/Toque model/Loss/A/C Compressor to see if they are the same as other cars that are the same year as yours.. Is this an all factory car? Changes to the intake, or throttle body, or?

[trocc4]

It originally didn't have ram air, it does now. It has the factory intake and throttle body. Also I have a factory tune from the repository for the same year vehicle. Attachment of the factory tune on left mine on the right they are different.

[HATEHPTUNERS]

In my mind, the ONLY way the engine RPM is increasing on A/C turn on is if the PCM is commanding it.. Otherwise, just turning the A/C on will usually result in a LOWER engine idle-as evidenced on carb equipped vehicles that DO NOT have an A/C solenoid that bumps idle. It HAS to be that the PCM is adding air-either through the IAC, or some other parameter.. If you are monitoring all the air channels hopefully you can see where the added air is coming from, and then work backwards from there. If the IAC counts increase right at A/C Turn on-you KNOW for sure that the increased idle is being commanded by the PCM. You know there is a channel for "A/C Request" right? You can actually monitor when you turn the A/C on so that it can be easily/readily witnessed in the scan log. That Torque Model that you searched, I don't fully understand how that affects engine RPM/IDLE, but I know for sure that it does. I have an LS swapped 94 Silverado that would essentially act like it was on cruise control when you turned the A/C on while driving down the road.. Seriously, it would hold 80+MPH with my foot off the gas.. As soon as I turned the A/C off, the truck would then start slowing down normally. Whichever of the two tables that you posted above has the LOWER settings, maybe try changing to those settings just for a test, burn it, test it, and see if that fixes it. Worse case, you can go back to what was there previously if it does not fix it, or makes it worse. I still think a good scan log of ALL the air channels to include IAC requested, IAC actual, A/C request, and all the usual stuff, and you will be able to see where the extra air is coming from. I don't think the PCM is adding spark at A/C turn on because it looks like the PCM is actually pulling spark trying to control the engine rpm. Anyway, please post back your results as I'd like to know what and how you end up fixing it. Makes it easier for people with this same problem in the future when they find posts like this that have the "fix".

[trocc4]

will do thanks

[trocc4]

Ok finally changed the parameter numbers in the engine / torque model /loss with no change after driving 5 miles idle shot up to 1,300 rpms

[DillyBar]

Ok finally changed the parameter numbers in the engine / torque model /loss with no change after driving 5 miles idle shot up to 1,300 rpms

Has anyone figured this out? I am having the exact same issue down to the car 99 trans am fbo cam and car will drive and idle fine but intermittently when I turn on the ac it will shoot up to 2-2500 rpm and act like it has cruise control on until I turn it off then it is fine again

[SiriusC1024]

Without being able to see the tune to make sure everything is setup right, I'd have to say turn off Spark>Advance>AC Bump Tq Spark.

[DillyBar]

I was going to try that today after work. I have attached the tune file and the log file.
the log file isn't great and I will try to get a better one later but at the 10-48 second mark you can see the that I have 0% throttle with the ac on and it will just idle around 2000 RPM


5-10-24 AC High Idle.hpl5-10-24.hpt

[SiriusC1024]

Looks like a vacuum leak.

[DillyBar]

I thought that as well but the issue is intermittent. I sprayed brake clean around the engine and behind where the vacume port is for the ac controls with and without ac on and no change. I drove it to work this morning with the ac on full blast but I could not get it to do it I am really at a loss with what to do.

[edcmat-l1]

That idle roll at the end of the log looks like it doesn't know it's idling. I see your TPS voltage but no TPS %. Add that and log it again.

Also, you have it in "maf only" mode and these PCMs don't work like that. You need to dial in the VE properly and set the Dynamic airflow able/disable back to stock.

I'd bet between the 2 it'll clean up what it's doing.

[Alvin]

add short term and long term idle trims also LTIT STIT get plenty of log with it completely stopped.

[DillyBar]

For sure I will get those added to my logs!

[DillyBar]

That is weird Tps % is on that log and only showing a percentage sometimes every other log i have of the car it works fine but I will say when it does the high idle with ac on it will do it if its at 0% or just cruising around 10%. A little bit of back story I brought the car once I got it together to a "reputable" local tuner car has fbo tsp ms3 cam, fast 102 and fast 102 throttlebody he had trouble getting it to idle correctly but once he had the idle "right" he put it on the dyno the car made 389 whp but he said I ran out of injector and needed new injectors and that he had tuned it in maf only. So long story short after a few text exchanges he no longer returns my calls/texts So I have been fighting these issues for about a year now. I am tired of relying on tuners and would like to know how to be able to do this myself so I am very new. So back to your original message from what I understand the main VE table is dialed in from this tuner (I could be wrong) I do have an afr guage and when I'm doing a pull afrs look good in the 12.6-13 range when Cruising they are leaner around 15.0 range. So you are saying set the dynamic airflow table back to stock? Sorry if I'm not fully understanding.

[SiriusC1024]

I do have an afr guage and when I'm doing a pull afrs look good in the 12.6-13 range when Cruising they are leaner around 15.0 range. So you are saying set the dynamic airflow table back to stock? Sorry if I'm not fully understanding.

That's why I said vacuum leak. Brake cleaner trick doesn't always work. As MAP increases the effect of a vacuum leak diminishes. See the trims? Think the tuner left it like that? Extra air>extra fuel>extra spark = high idle.

If the valley cover bolts weren't replaced with button heads then it's probably the intake manifold gaskets or cracked intake.