rough idle help please
Thread Starter
Instructor
Joined: Sep 2018
Posts: 244
Likes: 21
From: Tampa, Fl
rough idle help please
Hey guys, I'm sure this thread possibly exists somewhere already but I haven't found it. So I bought a 2009 A6 about 6 months ago now and I've been noticing a rough idle ever since I bought it. I thought this was normal as I've never owned a vette before but then one of my car friends hopped in and said it was possibly misfiring. The car will idle regularly and then shakes a bit every few seconds with the rev needle moving a tad bit. Yesterday I got a P0300 code too (random misfiring), I took out my MAF and cleaned it hoping that might be the issue but its still idling rough, I checked the spark plugs and the wires and they're both in good shape. Any thoughts?
Melting Slicks
Joined: Dec 2013
Posts: 2,232
Likes: 315
From: Bridgewater New Jersey
Look and listen for any arcing to ground at the coils packs and spark plug wires when the idle is rough. It will sound like a high pitch ticking noise. Best to look at night or low light, easier to detect, while the engine is running, obviously.
Melting Slicks
Joined: Sep 2017
Posts: 2,396
Likes: 525
From: Lower New York
The P0300 code is a generic misfire code when read on a cheap scanner. Use a better scanner and it will tell you exactly which cylinder is misfiring (P0301, P0302 etc..). Makes you job a lot easier to find it.
Le Mans Master
Joined: Jun 2008
Posts: 8,255
Likes: 411
From: Mt. Sinai NY
Hey guys, I'm sure this thread possibly exists somewhere already but I haven't found it. So I bought a 2009 A6 about 6 months ago now and I've been noticing a rough idle ever since I bought it. I thought this was normal as I've never owned a vette before but then one of my car friends hopped in and said it was possibly misfiring. The car will idle regularly and then shakes a bit every few seconds with the rev needle moving a tad bit. Yesterday I got a P0300 code too (random misfiring), I took out my MAF and cleaned it hoping that might be the issue but its still idling rough, I checked the spark plugs and the wires and they're both in good shape. Any thoughts?
Clif
Le Mans Master
Joined: Jan 2008
Posts: 6,457
Likes: 297
From: corpus christi Texas
Hey guys, I'm sure this thread possibly exists somewhere already but I haven't found it. So I bought a 2009 A6 about 6 months ago now and I've been noticing a rough idle ever since I bought it. I thought this was normal as I've never owned a vette before but then one of my car friends hopped in and said it was possibly misfiring. The car will idle regularly and then shakes a bit every few seconds with the rev needle moving a tad bit. Yesterday I got a P0300 code too (random misfiring), I took out my MAF and cleaned it hoping that might be the issue but its still idling rough, I checked the spark plugs and the wires and they're both in good shape. Any thoughts?
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Melting Slicks
Joined: Dec 2013
Posts: 2,232
Likes: 315
From: Bridgewater New Jersey
Thread Starter
Instructor
Joined: Sep 2018
Posts: 244
Likes: 21
From: Tampa, Fl
Spark plugs were all changed at around 101,000 with ACDelco 41110
Race Director
Joined: Jul 2005
Posts: 12,045
Likes: 3,587
From: Central MO
Since you have recently replaced plugs, you could have cracked one. It's sometimes not easy to see. I agree that you need to determine which specific cylinder(s) are causing the misfire to help narrow your search down. Beyond replacing plugs, plug wires and coils could also be bad. Once you narrow down the specific location for the misfire you then attempt to narrow it down to the specific cause.
Last edited by BadAV; Jan 24, 2019 at 07:36 AM.
Melting Slicks
Joined: Dec 2013
Posts: 2,232
Likes: 315
From: Bridgewater New Jersey
If this is the case, the OP can bring the car to most any auto parts store and may be able to narrow the misfire down if history is stored. They usually do not charge to read the codes.
Thread Starter
Instructor
Joined: Sep 2018
Posts: 244
Likes: 21
From: Tampa, Fl
I originally had the code checked at Advanced autoparts which is where the person who read the code gave me p0300
Melting Slicks
Joined: Jan 2008
Posts: 2,730
Likes: 159
From: Ventura CA
My car had a random rough idle and never triggered a code. I replaced the plug wires with a good aftermarket set and it hasn't had a rough idle since. If those wires are original I would replace them as they get baked in that engine compartment.
Le Mans Master
Joined: Oct 2005
Posts: 6,652
Likes: 2,106
From: Left Coast, San Diego
Hope you get it figured out. My 2010 base has 50,000 miles and has had a slight miss since I got it. No codes thrown. I replaced wires and plugs at 40,000 miles just hoping. Still misses. I checked the alternator lead in case it was to close to the plug wire. No help.
Thread Starter
Instructor
Joined: Sep 2018
Posts: 244
Likes: 21
From: Tampa, Fl
I might as well replace the wires and see, ill have an update in a few hours, crossing fingers this is it, the idle inst really all that rough it just jumps intermittently from 500rpm to around 600 or 650 at the worst every few seconds
Melting Slicks
Joined: Sep 2017
Posts: 2,396
Likes: 525
From: Lower New York
If 500rpm is your starting point and jumps to 600-650 I would think that alone could be cause for concern. 625-650 seems to be the sweet idle spot for most LS3 owners.
Burning Brakes
Joined: Aug 2018
Posts: 1,030
Likes: 219
From: Fredericksburg VA