aces04

I will be bringing my C5 in for the third time to try to resolve a rough idle problem. The first two visits to my dealership their mechanic only
checked for engine codes and found none. They tell me that the car idles fine. I disagree! How smooth should my C5 run? At idle, hot or cold, I can feel the engine idling with an occassional shutter/shake.
The exhaust note also indicates a roughness at idle. Has anyone else had their car in for this problem? If so, was the problem corrected and most importantly how was it fixed? I need some ammunition to throw at the mechanic. My patience and loyalty is running out!

VetteTech81

I would check the condition of the bellows between the maf and intake, check for any false air leaks after the MAF sensor... possibly the 02's are a little slow and degraded.. there are many things that can cause a rough idle... just because there are not any codes stored it doesn't mean there is not an issue.. codes are clues to helping find a problem.... thats all they are.. pluging in does not tell you what is wrong with the car.. it is a diagnostic tool which helps point the tech in a direction to further diagnose..
-=Rick

vizette

I would change the plugs and possibly the plug wires and see where you're at after that. If it's high milage, maybe a decarb (i.e. seafoam) before the plugs.

I dunno about others, but mine has a minor "tremble" at idle. If I ever get a new cam it'll be more than minor

-Rich

jerrypc

i have the same EXACT problem with my 99 C5, can't seem to track it down. My mechanic says its normal too, but I also disagree.

MARLTON LT-4

I just picked up a '04 and I noticed the same thing. At our last club meeting we put 3 C5's together around the same year, all stock, etc. The two with 15K and under had a rougher idol compared to the one w/40K on it. MAYBE this the difference??

CP

msghuff

you need to check the plugs. The stock platinum "pucks" come off and the gap opens up and can cause a rough idle. very common problem with the ac-delco platinums. A good amount of rough idling problems can be tracked to ignition systems. When both my C5's were new they still didnt idle smooth as glass. A slight amount can be expected due to the cam profile. Even stock its fairly agressive compared to previous generations.

Jeff Jeff

Mine has always shook some when idling (stock). I would venture to guess it is normal, but it depends on how much shaking you are talking about. You are not going to get the smoothness of a lexus if that is what you are after.

Dan_the_C5_Man

It's most likely normal, these LS1 motors DO NOT run smoothly at idle, mine does the same thing; new plugs / new wires / old plugs / old wires / whatever.

dwilcox

I suddenly had the same issue a while back. Just a little "bumping" at the light, nothing major it just bugged me. My dealer, whom I trust put in new plugs and wires. He then asked me if I was using any fuel additive. To which I had to reply that I was using the 104 Octane Booster on a regular basis. He said that is OK if you add it and run the tank out, on occasion but not to add it and let it set in the tank for any period of time. He said any extended use will eat up a portion of the plug, which he showed me. Long story short, my bet is that it is your plugs and wires. My 01 only had 31K when this happened. Been smooth as silk ever since which has been about 4500 more miles.

C5_Roadster

i have the same issue

Point & Shoot

I posted a rough idle thread a couple of weeks ago and here's what worked for me (plugs and wires were new and tight).

My local dealer has a great mechanic who works directly with me to diagnose problems.

We did these one by one in this order (my car has 55K miles):

- fuel injector cleaning

- my throttle body was nasty looking on the inside - rather than cleaning it, I swapped it out with a ported and polished unit done by a local shop

- changed fuel filter

- my belts and belt tensioners were shot (55K miles) and causing all kinds of noise and vibration (tensioners under warranty)

She runs like a champ now - very smooth at idle with only a slight tremor which is normal for these cars.

And as far as power is concerned, WOW I feel a noticable difference with the new throttle body - power builds much smoother & faster than before.

I hope this helps.

LFZ

glad i'm not the only one either...got the same problem, and my 03 A4 vert only has 10,000 miles on it.