High idle no check engine light?
05-01-2018 | 12:52 AM
#1
Thread Starter
Teching In
Joined: Apr 2018
Posts: 19
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From: Castro valley ca
High idle no check engine light? (LS1 M6)My idle is at 1050 RPM’s. If I give a little gas the rpm will drop to normal and then right away go back to 1050rmps. It started right after I put new spark plugs. I did a smoke check and seemed fine. And I just put a new MAF sensor and that fixed my other issues on the trans am.
I also cleaned the Air Flow Sensor. Didn’t help.
Any info helps thanks guys!
I also cleaned the Air Flow Sensor. Didn’t help.
Any info helps thanks guys!
05-01-2018 | 12:55 PM
#2
Joined: Nov 2001
Posts: 32,386
Likes: 1,813
From: Schiller Park, IL Member: #317
With stock tuning, the M6 idle speed should be commanded to 800rpm. The stock tach is not always 100% accurate on these cars, so if you're seeing that "1050" on the tach, it may actually be a different number on a scanner. If the idle rpm hangs too high for too long, you should see a P0507 code. Are you getting any SES for this? I think it trips at about the ~150-200rpm above commanded idle speed point.
As for basic checks, have you verified that the throttle cable/linkage isn't binding on anything?
There are some simple things you can check with a scanner to get a better idea of what might be happening, such as IAC (Idle Air Control) count. If the IAC count is at 0 (closed), and the idle speed is commanded to 800rpm (as it should be) but is actually shown (via the scanner, not the tach) to be higher than 800, then air is entering from somewhere that it shouldn't be (or the IAC is stuck partially open/unable to close fully, meaning that it might need to be cleaned or replaced). Smoke check may not reveal a leak if it's "internal" (meaning EVAP system allowing too much flow, or EGR system allowing flow when it shouldn't; the latter would more likely set a code and be a more pronounced issue, though this would not necessarily be true of the former). Depending on the various scanner data, there could be an issue with the TPS (Throttle Position Sensor) as well (you'd want to look at TPS voltage and percentage at idle).
As for basic checks, have you verified that the throttle cable/linkage isn't binding on anything?
There are some simple things you can check with a scanner to get a better idea of what might be happening, such as IAC (Idle Air Control) count. If the IAC count is at 0 (closed), and the idle speed is commanded to 800rpm (as it should be) but is actually shown (via the scanner, not the tach) to be higher than 800, then air is entering from somewhere that it shouldn't be (or the IAC is stuck partially open/unable to close fully, meaning that it might need to be cleaned or replaced). Smoke check may not reveal a leak if it's "internal" (meaning EVAP system allowing too much flow, or EGR system allowing flow when it shouldn't; the latter would more likely set a code and be a more pronounced issue, though this would not necessarily be true of the former). Depending on the various scanner data, there could be an issue with the TPS (Throttle Position Sensor) as well (you'd want to look at TPS voltage and percentage at idle).
05-01-2018 | 08:58 PM
#3
Thread Starter
Teching In
Joined: Apr 2018
Posts: 19
Likes: 0
From: Castro valley ca
With stock tuning, the M6 idle speed should be commanded to 800rpm. The stock tach is not always 100% accurate on these cars, so if you're seeing that "1050" on the tach, it may actually be a different number on a scanner. If the idle rpm hangs too high for too long, you should see a P0507 code. Are you getting any SES for this? I think it trips at about the ~150-200rpm above commanded idle speed point.
As for basic checks, have you verified that the throttle cable/linkage isn't binding on anything?
There are some simple things you can check with a scanner to get a better idea of what might be happening, such as IAC (Idle Air Control) count. If the IAC count is at 0 (closed), and the idle speed is commanded to 800rpm (as it should be) but is actually shown (via the scanner, not the tach) to be higher than 800, then air is entering from somewhere that it shouldn't be (or the IAC is stuck partially open/unable to close fully, meaning that it might need to be cleaned or replaced). Smoke check may not reveal a leak if it's "internal" (meaning EVAP system allowing too much flow, or EGR system allowing flow when it shouldn't; the latter would more likely set a code and be a more pronounced issue, though this would not necessarily be true of the former). Depending on the various scanner data, there could be an issue with the TPS (Throttle Position Sensor) as well (you'd want to look at TPS voltage and percentage at idle).
As for basic checks, have you verified that the throttle cable/linkage isn't binding on anything?
There are some simple things you can check with a scanner to get a better idea of what might be happening, such as IAC (Idle Air Control) count. If the IAC count is at 0 (closed), and the idle speed is commanded to 800rpm (as it should be) but is actually shown (via the scanner, not the tach) to be higher than 800, then air is entering from somewhere that it shouldn't be (or the IAC is stuck partially open/unable to close fully, meaning that it might need to be cleaned or replaced). Smoke check may not reveal a leak if it's "internal" (meaning EVAP system allowing too much flow, or EGR system allowing flow when it shouldn't; the latter would more likely set a code and be a more pronounced issue, though this would not necessarily be true of the former). Depending on the various scanner data, there could be an issue with the TPS (Throttle Position Sensor) as well (you'd want to look at TPS voltage and percentage at idle).