How do I start diagnosing?
At 107K could I maybe need engine mounts?
Thanks in advance.
How do I start diagnosing?
Can you explain more on the vibration… is it speed related I know you said RPM related. what if your coasting…
If I accelerate even while car is standing in park, as soon as I get to 2500 I feel it. Could it be bad/dirty injector?
It is definitely engine related.
Sorry I completely missed this.
If you have a vag com. That is a very useful took. Start by checking to see if there are any fault codes. The cool thing about vag com is it will give you the RPM of the faults with other supporting data.
Sounds like its something in the rotational assembly. Or that is where I would start. Look at the belt and the alternator with the crank pulley. See if anything stands out. With the limitation of what you can see.
Hey TomaS8, Just curious if you figured out what was causing the vibration in your S8?
My S8 started making a consistent vibration noise, more like a grinding noise, at exactly 2500 - 3000 rpm as well.
My serpentine belt shredded one morning while the car was warming up, decided to buy JHM’s light weight crank pulley and install it while I was going to be in there with the radiator off, replacing the belt.
First drive after installing the new belt and pulley, I noticed the vibration and loud grinding sound at exactly 2500 - 3000 rpm, it goes away after 3000 rpm or before 2500. Also, it doesn’t happen when I’m in park or neutral revving the engine, only when in drive.
Figured I’d come here with questions first as your symptoms are super similar to mine.
The intake manifold change over happens in slow to medium speeds in that 2500 range. In some cases the tumble flaps do the same.
Check the intake manifold and also see if you can get this to happen in neutral.
Either way I would inspect the intake manifold to see what is going on just to eliminate that from the mix.
I bought the car with the intake manifold flaps deleted. I’ve put roughly 2k miles into it since, never had that grinding/noise before. The noise is clearly loud, and you can also feel it in your foot at the gas pedal
and it doesn’t happen in neutral, my first thought was to have someone hold a screw driver against different parts and listen as I revved in neutral, but it only happens when in gear at 2500 - 3000 rpm, accelerating and decelerating.
If the belt shredded and flew off it could have caused some damage to the idle pulley. The vibration might be from the idler. Usually when the pulley is out of alignment you get a grinding noise and it would be under load that the tensioner gets more use. Might be worth just taking a look at the front of the motor while the car is running.
Yea that was my first guess too, when I bought the belt to replace it, I also bought JHM’s light weight crank pulley to throw in while I had everything off anyway, got it all back together, then noticed the noise for the first time, pulled it all back apart and rechecked all the pulleys, the idler pulley sounded like it had some bad bearings, so I ordered a new one and replaced that as well.
Now that I think about it, I remember the tensioner pulley had a slight wobble to it, but other than that it seemed fine. You think a minor wobble could cause some grinding noises under load?
Its very possible. You really need to jack up the car pull the belly pan off and crawl around under the car in the front of the motor looking to hear if something stands out.