LS1 idle?
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,308
Likes: 3,924
From: Cape Coral, Florida
Le Mans Master
Joined: Jul 2010
Posts: 5,954
Likes: 711
Back to the dealer or a local tuner. It's through the computer. Might be a vacuum leak?? If this is how it's been, them need to adjust computer.
Safety Car
Joined: Jun 2017
Posts: 4,786
Likes: 425
From: North Georgia, USA
is the MIL (SESL or CEL) on? What DTCs are active?
You will need a scan tool or OBD-II Bluetooth dongle with a scan app to diagnose and repair a high idle issue. There's a PID for "desired idle RPM" available in the live data stream. It might be called "target RPM," or "commanded RPM," or something like that. It's usually pretty obvious as the RPM the computer wants the engine running at. Compare that with the actual engine RPM in the data (pay no attention to the gauges in the dash). You'll see one of two conditions.
Most common is the computer wants a low RPM (often around 700 RPM) and the engine is running too fast. That's usually a vacuum leak allowing unmetered air into the engine. If that's what you have, I can post some tips for finding those leaks.
The other situation is where the computer is trying to run the engine at a high idle. This will show the "desired RPM" (whatever your scanner calls it) is high, and the engine is running at the correct high idle speed. That's usually caused by a failing temperature sensor. Either the coolant temperature sensor or the intake air sensor can fail and read extremely cold. Look at those temps in the OBD-II live data. I've seen readings below -50 when sensors (or sensor wiring) fail.
Last edited by C6_Racer_X; Jun 7, 2020 at 09:35 AM.
Thread Starter
Drifting
Joined: Apr 2014
Posts: 1,396
Likes: 129
From: Plainfield IN
There is no mechanical adjustment for idle speed. It's handled by the computer.
is the MIL (SESL or CEL) on? What DTCs are active?
You will need a scan tool or OBD-II Bluetooth dongle with a scan app to diagnose and repair a high idle issue. There's a PID for "desired idle RPM" available in the live data stream. It might be called "target RPM," or "commanded RPM," or something like that. It's usually pretty obvious as the RPM the computer wants the engine running at. Compare that with the actual engine RPM in the data (pay no attention to the gauges in the dash). You'll see one of two conditions.
Most common is the computer wants a low RPM (often around 700 RPM) and the engine is running too fast. That's usually a vacuum leak allowing unmetered air into the engine. If that's what you have, I can post some tips for finding those leaks.
The other situation is where the computer is trying to run the engine at a high idle. This will show the "desired RPM" (whatever your scanner calls it) is high, and the engine is running at the correct high idle speed. That's usually caused by a failing temperature sensor. Either the coolant temperature sensor or the intake air sensor can fail and read extremely cold. Look at those temps in the OBD-II live data. I've seen readings below -50 when sensors (or sensor wiring) fail.
is the MIL (SESL or CEL) on? What DTCs are active?
You will need a scan tool or OBD-II Bluetooth dongle with a scan app to diagnose and repair a high idle issue. There's a PID for "desired idle RPM" available in the live data stream. It might be called "target RPM," or "commanded RPM," or something like that. It's usually pretty obvious as the RPM the computer wants the engine running at. Compare that with the actual engine RPM in the data (pay no attention to the gauges in the dash). You'll see one of two conditions.
Most common is the computer wants a low RPM (often around 700 RPM) and the engine is running too fast. That's usually a vacuum leak allowing unmetered air into the engine. If that's what you have, I can post some tips for finding those leaks.
The other situation is where the computer is trying to run the engine at a high idle. This will show the "desired RPM" (whatever your scanner calls it) is high, and the engine is running at the correct high idle speed. That's usually caused by a failing temperature sensor. Either the coolant temperature sensor or the intake air sensor can fail and read extremely cold. Look at those temps in the OBD-II live data. I've seen readings below -50 when sensors (or sensor wiring) fail.
