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Idle Glitch ??

 
Old 05-14-2019, 02:23 PM
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Dave in Pa
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Default Idle Glitch ??

Have only driven my new to me Vette twice, brought it home in the rain and then again to go get state inspection. (dry that day) Has 31,000 miles & well maintained. Now back surgery 3 days ago so it will be a bit before driving it again. Once it is warmed up and when sitting at an idle stopped, it seems every 30 seconds or so to shudder or sorta torque roll to the right (feel it in the seat) and yet no discernible change on the tach that I can see.If the RPM is changing I cannot see it or hear it. As I left the shop I mentioned it to my mechanic and he said maybe clean the TBI and or MAF also. It has no effect when going down the road in any gear when I then sorta found out how quick this car is!! Any ideas/opinions as I seat here recuperating?? Thanks, Dave
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Old 05-14-2019, 03:28 PM
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ArtClassShank
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A bit of "shiver" is normal, check your codes and maybe clean the MAF anyways for peace of mind. If you want to go all the way, plugs, plug wires and maybe a replacement air filter.

These cars are not silky smooth, it's a sports car, you're going to get some feedback.

I've driven 2 <1 year old C7's and they also have a bit of a rumble.

Last edited by ArtClassShank; 05-14-2019 at 03:29 PM.
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Old 05-14-2019, 05:58 PM
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does it sort of seem to cut out for a millisecond but keep on running?
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Old 05-14-2019, 06:08 PM
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Rob 02
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Does it do it after the engine has warmed up? On a cold start the PCM needs time to adapt to the environment.
If you have a Z06, the cam is a little hotter and will always have a little shutter during idle.
Higher performance engines don't idle as smooth passenger cars.
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Old 05-14-2019, 06:33 PM
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Dave in Pa
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Originally Posted by ncali View Post
does it sort of seem to cut out for a millisecond but keep on running?
MMMMM I don't think so because it acts more like the car is "rolling from the 12 o'clock position to the 1:oclock position. If the tach was going up 200 Rpm it would make sense to me; it is very rythmic and seems to happen consistently every 20 to 30 seconds. This is only after the temp is up to normal etc etc. Sorta reminds me of lopey cams & solid lifters of the 60's but not quite?? It so consistent on its timing; mechanic said maybe MAF letting it get lean?? I dunno...........Dave PS: Runs like a scalded cat though when I had the chance!!
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Old 05-14-2019, 07:22 PM
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Rob 02
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Could be a stuck hydraulic roller lifter.
You may have a broken spring
It is also possible that the bearing in one of the rocker arms has failed. You could listen for noises with a cheap mechanics stethoscope.
I know that the valve-trains in these cars are kind of noisy any way but a damaged rocker lifter or spring would have a louder metallic sound (like a screw driver tapping on a bench).

What year is your car. Some years were prone to certain problems.
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Old 05-14-2019, 07:27 PM
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Dave in Pa
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It is a 2001 Vert 6 speed, 31000 miles. Now you have me worried!!

Last edited by Vetteman Jack; 05-17-2019 at 01:12 AM.
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Old 05-14-2019, 08:08 PM
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Originally Posted by Dave in Pa View Post
It is a 2001 Vert 6 speed, 31000 miles. Now you have me worried!!
I doubt it is that bad but the possibility exist. I would still put my ear on a long screwdriver and listen to the valve cover for noise. Even if it is one of these parts that failed, they are not as hard to replace as you may be thinking.

You may just have bad fuel, dirty injectors or possible fouled plug.

There is an ignition coil wiring harness on each side of the engine. If one of them got wet, is loose or corroded it could make the engine want to push to one side. You could check the connectors for corrosion.
I'm curious as to why you are not throwing a misfire or knock sensor code.

AFIK it was the Z06 LS6 that had valve spring issues not the LS1 base coupe/ vert.
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Old 05-14-2019, 08:18 PM
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Dave in Pa
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Thanks a lot for all the advice Rob, yeah no codes at this point. In a week or so when I am able t drive it I will have my mechanic check all the above and we will start a process of elimination I guess. Got all the previous maintenance paperwork organized so now I know what has and has not been done. I will post back what I/We find!! Dave

Last edited by Vetteman Jack; 05-17-2019 at 01:12 AM.
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Old 05-14-2019, 08:33 PM
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How long has the gas has been in it?

Last edited by Rob 02; 05-14-2019 at 08:58 PM.
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Old 05-14-2019, 08:46 PM
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Originally Posted by Rob 02 View Post
How long the gas has been in it?
When I picked it up on 4/22/19 the owner had just done 30K checkup and topped it off with gas. It did the idle/shake thing driving home that day. She would only use Top Tier gas, was adamant about it.
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Old 05-14-2019, 09:05 PM
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It's not good for a car to sit too long Did they mention any modifications?
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Old 05-15-2019, 10:12 AM
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You may have a misfire going on there...since you just purchased it and not knowing how often the PO drove it you may have a lean misfire...maybe a clogged injector...try throwing some Techron in the fuel tank the next few fill ups and see what happens...this can be MANY things going on...just speculating !!
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Old 05-15-2019, 10:38 AM
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Is this shudder happening with the AC turned on?
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Old 05-15-2019, 11:20 AM
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Dave in Pa
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Originally Posted by Rob 02 View Post
It's not good for a car to sit too long Did they mention any modifications?
Has Corsa exhaust, K&N intake and MGW shifter, thats it.
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Old 05-15-2019, 11:22 AM
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Originally Posted by C5 Diag View Post
You may have a misfire going on there...since you just purchased it and not knowing how often the PO drove it you may have a lean misfire...maybe a clogged injector...try throwing some Techron in the fuel tank the next few fill ups and see what happens...this can be MANY things going on...just speculating !!
Ok good, Techron it will be next time out!! Thanks!
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Old 05-15-2019, 11:23 AM
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Originally Posted by Turpid porpoise View Post
Is this shudder happening with the AC turned on?
On or Off, does not seem to matter or change what it does?!
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Old 05-15-2019, 05:06 PM
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Have you ever owned another LS car? The LS generation of GM V8's have a different firing order than the Gen I and Gen II's prior and it can produce what is at best a 'unique' idling profile, especially if all you've ever intimately been around is LT or anything of that order.

If you have pulled codes (you can do this yourself with the car's DIC. Google it and find the YouTube video), you have no codes relating to the PCM, and the car overall appears to be running right then either (1) the car has some sort of shelf tune you weren't told about (I doubt it with just a Corsa cat back and a K&N filter, since those really aren't power mods and throwing a tune at that wastes money) or (2) at the absolute worst there's some general maintenance items lacking. On my second point for example the car may only have 31K miles and the plugs are rated to 100K but the wires are rubbing and rubber over time deteriorates exposed even sitting in a garage. If deterioration occurs in spark plugs wires it increases resistance = lesser than ideal spark.
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Old 05-15-2019, 05:10 PM
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Rob 02
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^ Well put.

I was getting the feeling there was something the previous owner didn't disclose.

Last edited by Rob 02; 05-15-2019 at 05:14 PM.
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Old 05-15-2019, 05:38 PM
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I picked up my first C5 with 30K on it this year also and drove it 3 hours home. When I pulled off the exit and stopped at the light I experienced what I think you are experiencing. Thought at first it was going to shutter and die. But it kept going with that same type of rhythmatic pattern you describe. Had me wondering as well. Didn't think it was missing since it probably would have thrown a code and, like yours, it runs fine otherwise. After driving it more and getting used to it I just figure it is the nature of the beast as the vehicle has had no issues. I kind of like it now as it is reminiscent of the old idle 'loping' of previous muscle cars. I probably wouldn't fret about it too much while you are laid up until you are able to get more time behind the seat.
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