Hanging high idle when coming to a stop
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From: SF Bay
Hanging high idle when coming to a stop I have been chasing this issue for a few months now. I have a 1967 Camaro with a LS2 6.0L out of a 2007 TBSS, and replaced the intake manifold with the LS2 car intake and throttle body (along with MAP sensor). I have the 5 pin MAF connected along a straight section of DIY intake tubing (3.5" inner diameter). I have not connected the AC yet, so the compressor hasn't been turned on yet during driving. Long tube headers (Doug's) with front O2 sensors only. I have a T56 from a 2002 Camaro (supposedly) for the trans.
When I start the car, it runs about 900 rpm for 4 seconds, and them drops about 100 rpm (~800 rpm) and idles with a small amount of surge. When driving, and coming to a stop (shifted into neutral), the RPMs will hang around 2000 RPM for 2-3 seconds and then drop back to ~800 RPM. It is getting very annoying, and preventing me from driving it.
My tuner says that everything in the tune is correct, but I am not 100% sure that this is accurate (can't tune it myself as of now). Mechanically, I cannot find any vacuum leaks around the intake or upper half of the engine.
Any ideas??? All/any help would be greatly appreciated!!
When I start the car, it runs about 900 rpm for 4 seconds, and them drops about 100 rpm (~800 rpm) and idles with a small amount of surge. When driving, and coming to a stop (shifted into neutral), the RPMs will hang around 2000 RPM for 2-3 seconds and then drop back to ~800 RPM. It is getting very annoying, and preventing me from driving it.
My tuner says that everything in the tune is correct, but I am not 100% sure that this is accurate (can't tune it myself as of now). Mechanically, I cannot find any vacuum leaks around the intake or upper half of the engine.
Any ideas??? All/any help would be greatly appreciated!!
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From: SF Bay
Idle air controller on an LS2 is the throttle cracking, correct? I think the servo in the DBW opens the blade to allow additional air in when coming to a stop (or so I have read). My tuner said that this had the correct inputs into the table and shouldn't be the problem, but I can't 100% verify this.
Clutch pedal position has a switch that cuts to ground when the pedal is depressed (normally open when clutch pedal is not depressed). Is this correct?
VSS is connected to a speedometer (Speed Hut gauge) but I haven't calibrated the gauge yet. The Speed Hut directions tell me to map out a 2 mile drive, press the button at start, and then press again once I hit the 2 mile mark and I think it takes a count and stores it for MPH. Does this need to be completed? I didn't think there was any feedback into the ECM from the VSS (only an output).
Thanks for the tips guys!
Clutch pedal position has a switch that cuts to ground when the pedal is depressed (normally open when clutch pedal is not depressed). Is this correct?
VSS is connected to a speedometer (Speed Hut gauge) but I haven't calibrated the gauge yet. The Speed Hut directions tell me to map out a 2 mile drive, press the button at start, and then press again once I hit the 2 mile mark and I think it takes a count and stores it for MPH. Does this need to be completed? I didn't think there was any feedback into the ECM from the VSS (only an output).
Thanks for the tips guys!
Tom, what effect does the CPP switch have on hanging high idle when the clutch is depressed.
I had a similar issue in a manual trans car with the CPP switch eliminated. I was not able to solve it, except by changing out the ecu.
I had a similar issue in a manual trans car with the CPP switch eliminated. I was not able to solve it, except by changing out the ecu.
Idle air controller on an LS2 is the throttle cracking, correct? I think the servo in the DBW opens the blade to allow additional air in when coming to a stop (or so I have read). My tuner said that this had the correct inputs into the table and shouldn't be the problem, but I can't 100% verify this.
Clutch pedal position has a switch that cuts to ground when the pedal is depressed (normally open when clutch pedal is not depressed). Is this correct?
VSS is connected to a speedometer (Speed Hut gauge) but I haven't calibrated the gauge yet. The Speed Hut directions tell me to map out a 2 mile drive, press the button at start, and then press again once I hit the 2 mile mark and I think it takes a count and stores it for MPH. Does this need to be completed? I didn't think there was any feedback into the ECM from the VSS (only an output).
Thanks for the tips guys!
Clutch pedal position has a switch that cuts to ground when the pedal is depressed (normally open when clutch pedal is not depressed). Is this correct?
VSS is connected to a speedometer (Speed Hut gauge) but I haven't calibrated the gauge yet. The Speed Hut directions tell me to map out a 2 mile drive, press the button at start, and then press again once I hit the 2 mile mark and I think it takes a count and stores it for MPH. Does this need to be completed? I didn't think there was any feedback into the ECM from the VSS (only an output).
Thanks for the tips guys!
Would need to look at a pin out, but the clutch pedal position switch is about the same as a PNP switch on an automatic, and there are several strategies it controls as well...
I have used the Speedhut gauges, but that will have no bearing on what the PCM sees. Is your VSS connected to the PCM, or did you cut the wires and splice it into the speedo? Typically with electronic gauges, you would use the wire coming from the PCM/ECM to go to the speedo. The Computer needs the input from the VSS to tell where it's at, how fast, moving or setting still etc...could possibly be some of the problem....can be tuned out for different applications, but without knowing your entire setup, anything is possible.
T,
Last edited by TomM; Sep 22, 2016 at 08:32 AM.
I believe the CPP signal is to be grounded unless the clutch is depressed. Depressing the clutch will open the circuit.
I don't think this is your issue though since mine has never been hooked up at all.
I think Tom is onto something about the VSS. If it's not hooked to the PCM it could be the cause.
I don't think this is your issue though since mine has never been hooked up at all.
I think Tom is onto something about the VSS. If it's not hooked to the PCM it could be the cause.
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Thread Starter
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From: SF Bay
Thanks again for all the feedback, this is helpful!
The VSS is connected to the PCM, and my speedo is connected to the output from the PCM. So the PCM should be reading the VSS output from the T56 trans.
This also occurs when I am at a stop, I place it into 1st gear, depress the clutch a little to get the car rolling, press the clutch back in and the REVs jump up to 2k for 1-3 secs then drop back down.
The VSS is connected to the PCM, and my speedo is connected to the output from the PCM. So the PCM should be reading the VSS output from the T56 trans.
This also occurs when I am at a stop, I place it into 1st gear, depress the clutch a little to get the car rolling, press the clutch back in and the REVs jump up to 2k for 1-3 secs then drop back down.
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Verdad Gallardo Maybe it is the ground reference appearing and disappearing then. I would switch that CPP to open when clutch is pushed and ground when released and see if it fixes your issue.
CPP opened vs closed will depends on the ecu and pins used.
https://ls1tech.com/forums/conversio...er-switch.html
https://ls1tech.com/forums/conversio...er-switch.html
Thread Starter
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From: SF Bay
garys_68, thanks for the tip!
Any idea what it should be for a 2007(LS2) or 2008(LS3) Corvette? I am using a custom wire harness with an E38 ECM.
Or if you could point me to wiring diagrams for these cars, I could trace them down.
Thanks again!
Any idea what it should be for a 2007(LS2) or 2008(LS3) Corvette? I am using a custom wire harness with an E38 ECM.
Or if you could point me to wiring diagrams for these cars, I could trace them down.
Thanks again!
On The Tree
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On our harnesses we normally don't have provisions for clutch at all. This doesn't cause an issue with anything as it's not needed during a swap. If you are certain there isn't a vacuum leak I would point some of it potentially to the tune then. I've messed with stuff in a file before that has caused a hanging idle when I incorrectly adjusted airflow tables. Just food for thought. I would also make sure the file used is for a manual and not automatic.
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From: SF Bay
jcvett56,
Thanks for the input! The harness I purchased included it on there. My tuner made sure that the manual option was selected in the tune. I don't know anything about the tuning of the air tables, but I did watch my tuner mess with ti for a couple hours trying to get it to idle correctly and stop the hanging idle. This is when he pointed it to a mechanical issue (vacuum leak). I could not find any leaks anywhere, and it seems weird that a leak would only occur or have an effect when coming to a stop by pressing in the clutch and taking a load off of the engine. I don't even need to be moving for this to happen, as by starting to put a load on the engine by releasing the clutch and then pressing it back down, the idle will increase and hang for a few seconds until settling back to normal idle.
Thanks for the input! The harness I purchased included it on there. My tuner made sure that the manual option was selected in the tune. I don't know anything about the tuning of the air tables, but I did watch my tuner mess with ti for a couple hours trying to get it to idle correctly and stop the hanging idle. This is when he pointed it to a mechanical issue (vacuum leak). I could not find any leaks anywhere, and it seems weird that a leak would only occur or have an effect when coming to a stop by pressing in the clutch and taking a load off of the engine. I don't even need to be moving for this to happen, as by starting to put a load on the engine by releasing the clutch and then pressing it back down, the idle will increase and hang for a few seconds until settling back to normal idle.
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From: SF Bay
At this point, I am open to any and all suggestions, and I will look at anything to make this stop. I just wanted to check as many options before I start throwing money at it and replacing part-by-part to locate a random leak or faulty part.
I would love it if someone could look at my tune and see if it is even remotely close to what it should be. I know it would be best to look at it on the car and see it running, but I am even willing to send the ECM somewhere for a second look.
I would love it if someone could look at my tune and see if it is even remotely close to what it should be. I know it would be best to look at it on the car and see it running, but I am even willing to send the ECM somewhere for a second look.
You most likely have a tuning issue.
I had the same problem, my tuner couldn't figure it out either. I switched ecus and it went away. There are a couple threads here on the same subject, but no one mentions the fix.
I had the same problem, my tuner couldn't figure it out either. I switched ecus and it went away. There are a couple threads here on the same subject, but no one mentions the fix.
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From: SF Bay
I investigated a bit this weekend.
When I start my car, it will idle at about ~900 RPM for 4 seconds, and then drop to about ~725 rpm. It is noticeable when this happens, almost like a load is put on the engine. I took off my air ducting to the intake so I could see the throttle body blades, just to see. I can see the blades appear to be stable (not moving) during the first 4 seconds, and then become unstable (fluttering) afterwards. Could it be possible that the throttle body I have is bad? Or would it more than likely be the tune?
When I start my car, it will idle at about ~900 RPM for 4 seconds, and then drop to about ~725 rpm. It is noticeable when this happens, almost like a load is put on the engine. I took off my air ducting to the intake so I could see the throttle body blades, just to see. I can see the blades appear to be stable (not moving) during the first 4 seconds, and then become unstable (fluttering) afterwards. Could it be possible that the throttle body I have is bad? Or would it more than likely be the tune?
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From: SF Bay
https://vimeo.com/185339575
Here is a video I took of the throttle body. Around 20 seconds in (after I rev the engine), you can see the idle change and the blade start to flutter.
Here is a video I took of the throttle body. Around 20 seconds in (after I rev the engine), you can see the idle change and the blade start to flutter.
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From: SF Bay
I know this might be unorthodox, but would someone here have an extra LS2 Throttle Body that they would let me borrow to try and see if this is the issue? I would be willing to pay for all shipping/handling as well as put something up as collateral (not sure how, but willing) just to test it. If it worked, I'd be willing to buy it, if not, I would send it back unharmed.
Let me know if I am completely crazy....
Let me know if I am completely crazy....