I'm still getting used to my new to me 2004 coupe and all the noises and quirks that go with it. I tried searching before posting, but couldn't seem to find anything that matched my question.

When I'm sitting at a stop light (automatic trans), the car tends to shake subtlely and make some rhytmic noise. I'm guessing this is just normal for a V8 car (my first), but wanted to check in with others. My father in law owned the car before me, left it completely stock, and it has only 16,xxx miles on it.

The stock exhaust/engine almost sounds diesel like in the mornings too, but again I'm guessing this is normal?

 

Well firstly I have a MN6 and a slight vibration(s) in my car at idle is normal but not consistant...one time you will stop at lights and it will vibrate next lights smooth, could be fuel, engine temp. who knows as there are a thousand things being evaluated per second on the computer and it adjusts everything. Now the diesel noise when cold I would be concerned with as this sounds like piston slap to me...it is not normal for a tight LS1 to sound like a diesel..you can search piston slap and will have plenty of info on that topic, believe me. I am sure many more members will join in this topic. Good luck and welcome aboard the Corvette forum. Happy to have you aboard. Greetings, Rob

 

Thanks for the reply. The diesel noise may have been a bit too extreme a word to describe it. It's hard to put into to words a sound. It is certainly not a smooth sounding noise, but I'm coming from a 2007 Acadia that doesn't have the same sporting intentions as a 'Vette. So like I said I'm trying to determine what is "normal" for this type of car. My best bet is to get it in for service or meet with another local member so someone with a bit more experience with these cars can hear it first hand.

 

I have a low mileage 2003 coupe......and no subtle shaking or rhythmic noises at idle. In fact you can barely tell it is running.

As you suggested, you may want to have another C5 owner check it out, and/or have a service performed.

 

The first time I test drove a C5, I noticed the same thing. The car does have a slight shake when it's running. Not much, but if you have never been in a C5 you notice. I asked the dealer and he said they all run like that.

Then I bought one (different car than the test drive) and it does run exactly like the first one. I wouldn't worry too much but since the car is new to you it wouln't hurt to have someone do a once over on it.

I'll probably get flamed for this, but...call your Chevy dealer and ask if they have a mechanic there that specializes in Vettes. I did and was surprised to find that the guy really knew what he was doing.

Yes the dealer is expensive, but if they have a guy that works on all of their Vettes, he'll know right away if it's running right. Just be sure not to authorize any repairs in advance. The Chevy house knows how to take you to the cleaners. Almost any repair they recommend can be done at home for a sliver of the cost.

 

Every C5 I've ever been in has had a slight "shudder" at idle. That's just how they're setup with regards to the cam profile and tuning. It's completely normal.

The clatter of a Diesel engine is the best description of a sound similar to piston slap. It's sort of a hollow knocking sound coming from deep within the block. Also normal ... but it does vary from engine to engine, and it should subside once at operating temperature.

 

Your car should have a "clutch/decoupler" on the alternator pulley to address idle issues with the automatic. It may be working sometimes and others not. Just a thought. Have you pulled codes to see if there is anything else? My guess is that your car is working just fine.

PS: I assume it has an original alternator. If you need a picture of the one for your car let me know

 

MY2004 does the same, sometime a perfectly smooth idle at a stoplight, sometime a little rough. In searching postings it was suggested that the issue was plugs and or wires. I haven't got around to changing the plugs and wire but it hasn't gotten worse in the last year. No piston slap here

 

I have a stroker motor with a lopey cam. It has a nice, rhythmic vibration at idle. It makes you look for the slot to put a quarter into for more massage.

 

Have fun!

 

It's a little bit more profound when you have solid motor mounts!

I can see it in the side mirror.

 

I've been off this forum for the last few days, but I appreciate the new postings and comments.

As for the vibrations, the car just "shudders" to use someone else's words from side to side when sitting at a stop light.

dadaroo: No codes ever thrown to pull, original alternator. If you want to post the pic of the alternator, that would be great. I'll have to do more research on the "clutch/decoupler".

 

I've had my '03 Z06 since new. The engine has always been quiet and it does not visibly shake. However, when sitting in the car, it does have a pronounced vibration at idle, as if it has a big cam. OK, "big" is a bit of an exaggeration, but you get my meaning.

IMHO, it's part of the charm and completely in line with the sporting nature of the car. There are other manufacturers, the Japanese come to mind, who produce high performance automobiles that have no such character, if that is what you are looking for.

On the other hand, if you have a stock engine and the vibration is pronounced, it could be that the engine mounts have deteriorated. Any rubber part, be it a tire, belt, hose, wiper blade, or etc. will deteriorate over time, due to exposure to heat and the elements. You may wish to inspect the mounts, the next time that you crawl under the car to change the oil.

Another possibility is that some line, hose, or bracket is mis-positioned and transmitting the vibration into the body. These issues can be challenging to find and could very easily consume many hours of trial and error with a stethoscope, or a chassis ear.

Personally, I would be inclined to compare the car to other, similar examples, before embarking on a project. Good luck!

 

Normal

 

Would the decoupler have intermittent function. I have this same vibration at idle. Worse when completely warmed up and when AC is on and in gear with brake on. Goes away with the slightest increase in RPM. No vibration if AC is off or in park or neutral. I did take it to the dealer. They said the couldn't recreate the vibration. Any suggestions would be great.

Thanks in advance

 

All three of the C5s that I've owned has done the same thing. I took my '99 into a dealership in Nashville TN once and they informed me that the slight shaking at idle is perfectly normal. Never had any issues with it so I didn't worry about it after that.