just had a 2 quick questions, maybe someone has experience with this...
2004 Audi A8L 4.2

I am experiencing a light trembling/vibration at standstills and sometimes while driving. I notice it more at stop signs or at red lights. There is a light vibration that transfers through the seat and almost feels as if the seat alone is moving/vibrating.
Its not too noticeable unless you are seated and I feel it through the seats so its really annoying. I had a passenger in the car and he said he barely felt it but says its probably just cause its a V8. I don't think this is the case.

has anyone experienced any vibration in the car at a stand stills?
if the cars in neutral you feel it less.
and what might cause this.

Im taking the car in to get serviced next week so Id like to be able to have some knowledge before going in.

one more question...
every once in a while when turning the key to start the car, it wont start. a light comes on, EPC.
I'll have to turn the key back to the off position pull out the key and try turning to start again...then it starts with no problem. it happens intermittently, maybe every 1/20 starts
Ive been looking online and it seems that when this happens its usually either an old factory battery that should be replaced or in some cases its the crank sensor.
does any know if this sounds right or what this problem might be caused by?

thank you for your help.,..

 

What octane fuel are you using? It might be caused by the engine management advancing and retarding timing to prevent pinging when using a lower grade octane than usual, especially if the air conditioning is off (economy mode on).
Try filling up with higher octane fuel if you are not using the highest available currently.

 

Have been noticing a little extra vibration lately myself and run the highest octane gas available short of 'race fuel' we can get here.
My air is never on econ, and never on recirc - set to 20C (68F) year round.

Am hopeful it is just crap ethanol laced gasoline and the heat since this is my first summer with the car.

I've also noticed the temp gauge goes to center (normal running temperature) before getting through my first stop light.
Gut says it's not a coolant issue since the 75K service was done less than 5K miles ago.

Spied a mom & pop gas station the other day with a sign saying "No ethanol on pump 2".
May fill up there for a week or so to see if it makes a difference.

EPC is your fly by wire throttle IIRC.

 

I am in VA-USA, and have always used premium gas. I don't think its the gas but I have heard that it may be tranny mounts or maybe a torque converter.

 

Mine has always had a bit of a rough idle, especially if the air is off. The dealer's reply is that it's normal and about the same as other a* of the same vintage. I can even see my pass seat vibrate if no one is in it. I always run premium.

 

My car runs perfectly fine and always has. The vibration in the car is no more than in any other car I've owned/drove. If my passenger seat shook though I know I'd get it looked at by another person. Could be as simple as a throttle body clean or something along that nature. I have done all my prevent maint. too though. (fuel filter, all air filters, new plugs, etc.)

 

1. With rough running, run a dose of Techron through it. Either the 20 oz. bottle, or two of the 12 oz. ones. Classic Audi and other vehicle fix to minor running maladies to clean up intake system and valves.

2. How about...the spark plugs? You say it's a 2004. By now I expect it's been through at least one major service interval. What is the current life on plugs? If in doubt, consider changing. If you are familiar with reading plug condition, it can give you a good sense on how your internal motor condition is too.

3. Don't see it posted much on D3's as an issue, but what about the motor mounts? Are they in good shape? Electrically connected correctly, no codes, etc.? Long before I checked into this though, I would try #1 for about $12-15 and two minutes, and then #2 if it it seems warranted (from last plug change mileage) for the cost of plugs and intallation time/labor.