Slight rough idling
Thread Starter
6th Gear
Joined: Jan 2018
Posts: 6
Likes: 1
Slight rough idling
I am a new Corvette owner. I bought a used 2015 Z51 Stringray with 16K miles on it. When sitting idle it runs just slightly rough. Same when in neutral. Not real noticeable but its there. When I go above 1K RPM it goes away. Do you think this is an issue? Maybe I am just being to sensitive, but as with any mother with a new baby, any kick up is in question. Ha Ha.
Larry
Larry
Safety Car
Joined: Aug 2012
Posts: 3,960
Likes: 1,106
It is normal for the LT-1 and LT-4 engines. Actually most gas direct injected engines have a rougher idle than the port injected engines but the cam and other parameters gives them a noticeable "idle note" 
But the only way for you to know whether yours is normal is to compare it to another engine.
Listen carefully and you will also hear a ticking/clicking at idle which is from the high pressure fuel pump. It is driven by a separate lobe on the camshaft and will be loudest near the driver's side rear of the engine where it is mounted but the sound also radiates down the common fuel rails so it isn't full localized. Another entirely normal part of the gas direct injection system.
But the only way for you to know whether yours is normal is to compare it to another engine.
Listen carefully and you will also hear a ticking/clicking at idle which is from the high pressure fuel pump. It is driven by a separate lobe on the camshaft and will be loudest near the driver's side rear of the engine where it is mounted but the sound also radiates down the common fuel rails so it isn't full localized. Another entirely normal part of the gas direct injection system.
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 34,932
Likes: 12,344
From: NE South Carolina
I am a new Corvette owner. I bought a used 2015 Z51 Stringray with 16K miles on it. When sitting idle it runs just slightly rough. Same when in neutral. Not real noticeable but its there. When I go above 1K RPM it goes away. Do you think this is an issue? Maybe I am just being to sensitive, but as with any mother with a new baby, any kick up is in question. Ha Ha.
Larry
Larry
I am amazed that today's high performance engines can idle as smooth as they do. That is 460 hp under your foot from 376 cubic engines. Zora Duntov would have been elated to get 376 hp from 376 cubic inches in the day! Then with a very lumpy idle!
The C7 variable cam timing is a significant benefit it getting more torque and better low rpm performance. In addition all that with a lean running engine to keep pollution low. The big block 502 cubic inch carbureted engine in my street rod needs a rich mixture to idle at 950 rpm with a much rougher idle than the C7.
That all said -can't really define what you are experiencing as rough! Need to sit in a new Vette and see if it is the same! Go to a dealer and listen to the engine run and compare.
Last edited by JerryU; Feb 1, 2018 at 09:18 AM.
Melting Slicks
Joined: Dec 2017
Posts: 3,423
Likes: 539
From: 67401
It is normal for the LT-1 and LT-4 engines. Actually most gas direct injected engines have a rougher idle than the port injected engines but the cam and other parameters gives them a noticeable "idle note"
But the only way for you to know whether yours is normal is to compare it to another engine.
Listen carefully and you will also hear a ticking/clicking at idle which is from the high pressure fuel pump. It is driven by a separate lobe on the camshaft and will be loudest near the driver's side rear of the engine where it is mounted but the sound also radiates down the common fuel rails so it isn't full localized. Another entirely normal part of the gas direct injection system.
But the only way for you to know whether yours is normal is to compare it to another engine.
Listen carefully and you will also hear a ticking/clicking at idle which is from the high pressure fuel pump. It is driven by a separate lobe on the camshaft and will be loudest near the driver's side rear of the engine where it is mounted but the sound also radiates down the common fuel rails so it isn't full localized. Another entirely normal part of the gas direct injection system.
Safety Car
Joined: Aug 2012
Posts: 3,960
Likes: 1,106
Thanks NSC5 for this information. I too was wondering if my car's slightly rough idle and ticking/clicking at idle was normal or the sign of a problem. Up until this moment I chalked it up to "probably normal since my car has only 525 miles on it", but now I know the reason behind what I was feeling (slightly rough idle) and hearing (ticking/clicking at idle). Thanks NSC5.
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Le Mans Master
Joined: Jan 2006
Posts: 6,800
Likes: 2,653
From: Down south in Dixie
That's means she's ready to run. Enjoy that new car, and welcome to the forum Larry. And don't forget to use your best Corvette wave when you meet another member of the family. 
Enjoy that new car, and welcome to the forum Larry. And don't forget to use your best Corvette wave when you meet another member of the family.
Last edited by Rebel Yell; Feb 1, 2018 at 02:28 PM.