Author Topic: STII S/C cars with rough idle due to A/C compressor coming on (Read 9048 times)

TecSolOnt · « **on:** August 08, 2009, 10:33:15 AM »

Does anyone have specific knowledge on how to fix an issue with rough idle on STII supercharged cars when the A/C compressor comes on? I had no issues with this situation before the STII install. Talking to Dave he thought this would go away after a couple of hundred miles, it hasn't. I see on the Solstice forum others who have the STII experiencing the same issue.

I guess it comes down to the add'l load experienced by a 2.4L with the S/C installed when the A/C calls for the compressor. My take is if the A/C doesn't talk to the ECM then all the ECM can do is react to the load, thus a dip in idle and shudder.

Anyone know if there is a data transfer between the A/C and ECM that can allow the engine to speed up coincident with the load to prevent the engine shudder? Since it doesn't happen at all times with the A/C on I can't tell if it is just occurring at the point when your both at idle and a call goes to the compressor to turn on or if there are times this happens and there is no rough idle occuring. If the ECM and A/C aren't talking then I take it there is likely no fix if they do talk then it might be a software fix is needed.

Comments from the experts would be appreciated to understand this, thanks.

Critterman · « **Reply #1 on:** August 08, 2009, 11:50:12 AM »

I had the issue for a while, but it went away and hasn't come back with the st III

Jackknife · « **Reply #2 on:** August 08, 2009, 12:09:03 PM »

Mine does it sometimes. I don't consider it a problem. It sort of makes me remember engines with a hot, lopey cam that let you know at idle how much they've been "tweeked".

TecSolOnt · « **Reply #3 on:** August 09, 2009, 11:39:15 AM »

Quote

I had the issue for a while, but it went away and hasn't come back with the st III

Critterman did you mean to say it went away after awhile with the STII or did it go away after you had the upgrade to STIII done?

If it was after the upgrade to a STIII wonder if the tweeking of the engine code fixed it, shouldn't be any change to the engine load with the A/C on STII or STIII.

Critterman · « **Reply #4 on:** August 09, 2009, 01:09:59 PM »

On stII, it went away after I drove it for a while.

Helios · « **Reply #5 on:** August 09, 2009, 10:49:20 PM »

Mine still does it. It's been a few thousand miles now. It bugs me and i was planning on Dave or Randy hopefully addressing the issue at some time.

Critterman · « **Reply #6 on:** August 10, 2009, 09:00:49 AM »

do you have a spare ECM? Maybe something isn't correct in your tune.

Helios · « **Reply #7 on:** August 10, 2009, 11:17:02 AM »

Quote from: Critterman on August 10, 2009, 09:00:49 AM

do you have a spare ECM? Maybe something isn't correct in your tune.

No, i dont have a spare ECM. Yeah, i would like Dave and Randy to check the tune especially since the CAT crapped out shortly after the STII was installed.

Divingsolo (formely Randy@DDM) · « **Reply #8 on:** August 10, 2009, 07:50:43 PM »

tecsol and helios,
How many RPms does the engine drop when you turn on the ac? How many seconds does the drop last?

Helios · « **Reply #9 on:** August 10, 2009, 10:23:44 PM »

Quote from: Randy@DDMWorks on August 10, 2009, 07:50:43 PM

tecsol and helios,
How many RPms does the engine drop when you turn on the ac? How many seconds does the drop last?

Id say it drops to about 400-500 RPM lasting probably one sec maybe two before it recovers. Engine shudders and i'll occasionally have a loss in power steering for the same duration.

Divingsolo (formely Randy@DDM) · « **Reply #10 on:** August 10, 2009, 10:43:50 PM »

Quote from: Helios on August 10, 2009, 10:23:44 PM

Id say it drops to about 400-500 RPM lasting probably one sec maybe two before it recovers. Engine shudders and i'll occasionally have a loss in power steering for the same duration.

is this only when the a/c "kicks" on or just in general when coming to a stop with the a/c on?

Chemist · « **Reply #11 on:** August 11, 2009, 12:01:53 AM »

Randy,

Mine will occasionally drop to low (~500) RPM with the A/C on when I come to a stop, not always.

--Byron

Helios · « **Reply #12 on:** August 11, 2009, 05:49:25 AM »

Quote from: Randy@DDMWorks on August 10, 2009, 10:43:50 PM

is this only when the a/c "kicks" on or just in general when coming to a stop with the a/c on?

it's when i press in the clutch and the RPMs come down from a higher range when the AC is on.

Critterman · « **Reply #13 on:** August 11, 2009, 08:55:52 AM »

So it was in the high 90's yesterday when I left work. I used my A/C instead of putting the top down. As I sat in traffic waiting to leave the compound I paid particular attention to my idle. What I noticed is the load the A/C puts on the engine. My boost gauge usually reads 20" of vacumn at an idle, I was bouncing between 10-13" of vacumn. As soon as I touched the gas or engaged the clutch I was immediately in boost, at an idle anywhere from 0.2 -0.6. Without the A/C on I am normally in a vacumn state at this point.

driving down the highway maintaining 65, the hills where I normally go to a neutral state 0.0 vacumn/boost to maintain speed, I was boosting over 2 lbs to maintain. Any touch of the gas and I would be in boost. There was some minor fluttering when the A/C kicked in at an idle, some RPM loss but it recovered very quickly.

Don't know how that will help you guys with the problem, but it is just an observation.

GaryH · « **Reply #14 on:** August 11, 2009, 09:55:10 AM »

I don't think this has anything to do with the supercharger. Here's why I think so. I have an 07 N/A manual 5 speed and, like Helio, when I push in the clutch with the AC on, I get a shutter when the RPM drops to idle. My wife has an 08 automatic with a DDM stage ll supercharger. It doesn't shutter now, nor did it shutter before the supercharger was installed. I recall this shutter being discussed a long time ago on another forum. I think it either has something to do with the manual 5 speed or maybe it's something that was fixed on the 08 models. Of course this is just a guess on my part. And as many questions I've asked Dave and Randy, they can tell you that I don't know much.

TecSolOnt · « **Reply #15 on:** August 11, 2009, 10:17:46 AM »

Quote

I don't think this has anything to do with the supercharger. Here's why I think so. I have an 07 N/A manual 5 speed and, like Helio, when I push in the clutch with the AC on, I get a shutter when the RPM drops to idle. My wife has an 08 automatic with a DDM stage ll supercharger. It doesn't shutter now, nor did it shutter before the supercharger was installed.

I have a '06 automatic, has never shuddered with the A/C on until the night the Supercharger was installed. Dave suggested it was a known issue after the S/C was installed but would go away as the ECM learned the new setup. I know others like yourself have reported this shudder with non S/C cars. It has gotten somewhat better but still a issue on occasion, it was entirely coincident with the install of the S/C, I have enough miles and key turns since the install that it seems unlikely to completely go away now.

Dave , Randy any comment or insight on this?

nighttripper · « **Reply #16 on:** August 13, 2009, 12:39:02 PM »

I thought I read somewhere that the A/C will cut off if the car has a high demand for power, if this is the case I would think the ECM is involved somewhere

tazz · « **Reply #17 on:** August 13, 2009, 08:49:10 PM »

Even on the 2.0L when the A/C compressor engages it will drop the idle from 800RPM to 720RPM for a brief second then compensate back to around 800RPM do to parasitic loss of the A/C clutch engaging. Even with this compensation the idle is slightly rough but if the idle were to be increased by 25-50RPM to 825 or a bit higher to 850 will smooth it out.
With a S/C there is also a parasitic loss and could be compound the problem at idle. Not sure what S/C your using but the Eaton M112 on my Ford truck eats 5hp at idle.

TecSolOnt · « **Reply #18 on:** August 14, 2009, 12:40:57 PM »

I wouldn't be that concerned just to see the RPM drop as you indicated but the front end begins to shudder/shake as if the engine is about to stall at times. Odd that it is far from consistent just the rare time on my car , others report more often. Reports on the Solstice forum of idle dropping to 200 rpm at times with the SC installed by other owners. Not sure of the S/C I have either, installed by DDM. It seems a common issue with the STII.

Love the STII but it is a head shaker that this happens out of the blue infrequently. Never happened before the install of the S/C.

scdyne · « **Reply #19 on:** September 01, 2009, 12:16:02 AM »

I think this is an issue related to the AC torque compensation (1/2) tables [EFILive] or Idle AC Airflow Ramp (In/Out) Rate tables [HPT] depending on which application you are using.
Also if you are seeing boost at near idle then that could be causing the ECU to cycle between torque reduction cells in the AC Torque reduction table. Normally it's not going to be an issue, but anything above 90kpa causes this to happen. It would most likely only happen with a positive displacement S/C that can see boost at near idle conditions. Chances are a combo of IAT vs AC Torque and other tables above meet a specific set of parameters that both causes engine timing and AC torque load settings to enter conditions that normally would only be seen during non-idle conditions.
I have personally never seen a DDM tune so I can't say if this is the case, but I suspect this to be.

TecSolOnt · « **Reply #20 on:** September 02, 2009, 02:20:05 PM »

Thanks for the input, probably a little/lot above most of our heads. I did drop a note to Dave at DDM to see if meant anything to them with regards to the implications for the tune that comes with the S/C. No answer yet, just been a day, they are busy guys with the new shop and all.

Dave@DDMworks · « **Reply #21 on:** September 04, 2009, 11:19:56 AM »

Part of the issue with the idle droop has to do with the location of the throttle body on the PD supercharger setups. Since it is moved from the stock location to the back of the supercharger, we introduce a lot of throttled volume to the system. With the stock setup the computer can react a lot quicker to load changes at idle since only the intake manifold is the throttled volume. With the intercooled supercharger setup, the intake manifold, charge tubes, intercooler and supercharger all become throttled volume. So when the ECM needs to add air to the system for increase in load, it is heavily buffered by all that extra volume. We have been working for awhile on tweaks in the program to make the ECM respond quicker to this load difference, and have made minor improvements over time with it, but the extra volume in the system really makes it tough. Also different cars are more prone to it than others, some idle like champs and some take the little dip sometimes.

Helios · « **Reply #22 on:** September 04, 2009, 11:42:06 AM »

Dave, i've been wanting to come visit you guys. I have a small break in my work schedule from around the 14-18th this month. The car has been running great, but i'm getting some black smoke. I think that maybe im running too rich. When you guys installed my S/C my Cat was on the way out. Maybe this affected the tune? Maybe linked to my idle/shudder problem as well? Will you guys be able to work me into your schedule that week if i come up for a day or two?

Dave@DDMworks · « **Reply #23 on:** September 04, 2009, 11:55:25 AM »

I will be gone that week for an event, but I believe Randy will still be here and should be able to touch up your tune. I will check with him and let you know

Helios · « **Reply #24 on:** September 04, 2009, 12:17:41 PM »

thanks!

Dont hold me to it, cause i have a lot to do in 5 days before i have to be back on my jobsite. I have to get some elective surgery done, landscape the yard, and/or see you guys. So much to do...so little time.

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Author Topic: STII S/C cars with rough idle due to A/C compressor coming on (Read 9048 times)