Idle Speed

[CharlesBrown]

Can't find what this number should be. Search was not helpful. Under normal conditions i.e., engine warmed up, 60 to 80 degrees F etc. What should the idle speed be for the L98? Mine's all over the lot...700 to 1200 rpm. Worse, I get an engine speed-up with the clutch in during shifting. Thought this would reduce engine speed not increase it. Strange, with all the engine and performance data collected here there does not seem to be this fairly basic piece of data. Would someone please let me know what this speed should be. :confused

 

[gtawh]

Can't find what this number should be. Search was not helpful. Under normal conditions i.e., engine warmed up, 60 to 80 degrees F etc. What should the idle speed be for the L98? Mine's all over the lot...700 to 1200 rpm. Worse, I get an engine speed-up with the clutch in during shifting. Thought this would reduce engine speed not increase it. Strange, with all the engine and performance data collected here there does not seem to be this fairly basic piece of data. Would someone please let me know what this speed should be. :confused

1200 seems pretty high. mine usually idles between 600-700. maybe a problem with then throttle position sensor?

 

[CorvetteArchives]

Maybe the Idle Air Control Valve? Could be sticking... or there is a vacuum leak somewhere and its compensating for lack of pressure? Or even just a dirty throttle body?

 

[CharlesBrown]

If I'm to believe "Alldatra" the number should be 400/475, depending on trans.

 

[gtawh]

To me that seems too low. My car wouldn't stay running the few times it started up to that idle speed (replaced the relays behing the battery to fix that), but I have an automatic so maybe it's different for you

 

[CorvetteArchives]

way too low-400 to 475

It should be around 600

 

[Hib Halverson]

Can't find what this number should be. Search was not helpful. Under normal conditions i.e., engine warmed up, 60 to 80 degrees F etc. What should the idle speed be for the L98? Mine's all over the lot...700 to 1200 rpm. Worse, I get an engine speed-up with the clutch in during shifting. Thought this would reduce engine speed not increase it. Strange, with all the engine and performance data collected here there does not seem to be this fairly basic piece of data. Would someone please let me know what this speed should be. :confused

The idle speed spec is irrlevant.

The issue, here, is that the idle is unstable and the ECM cannot control it.

Fix that problem and the idle speed problem may go away.

Checking for vacuum leaks is a good place to start. More diagnostic info can be found in the factory service manual .

 

[Black Bart]

Usually when and engine hunts or wildly swings at Idle it is a vacuum leak.
Typically with a vacuum leak it will drop to 400 rpm then increase to 1200 or more.
Check for vacuum leaks be sure all connections to the TB and intake manifold are tight.

 

[CharlesBrown]

Here's the info. from my mechanic...
1200rpm okay when cold
700/800 after warm up
yes, the engine speed will "increase" when (clutch in) changing gears with the standard trans. but only briefly. Would go lower, but the average bear probably won't want to wait in between shifts 'till that takes place.

 

[CorvetteArchives]

....and the engine will go all the way to redline if you dont lift off the accelerator when engaging the clutch...

 

[CharlesBrown]

I didn't know that!

 

[CharlesBrown]

Amazing the things you can find out about here!

 

[vetteboy86]

Are there any codes stored? Maybe a stupid question, but Hib said it best, is that the real problem is the fact that the ECM cannot sustain a stable idle speed.

 

[CharlesBrown]

Using the "paperclip" jumper on the OBD showed normal i.e., flashing #12. Don't know what the mech. was seeing on the OBD-I but he seemed OK with the RPM's mentionmed above