Strong Vibration At 1600RPM-1800RPM and Idle.

[dizzysn]

Two months ago I noticed a vibration/shaking in my car at idle while in gear. It felt like an extremely rough idle, but the gauge was steady, and VCDS didn't show anything, save for an irrelevant CAN bus error.

I trade daily duties with another vehicle, and the S4 sat for two weeks. After swapping back out, I now noticed the same symptoms around 1600-2000k RPM on acceleration every so slightly. Once I'm cruising there's absolutely no vibration at all.

However, it's EXTREMELY noticeable on decel, at the same RPM range, to the point that I can feel it in the steering wheel, seat and floor well. Like if I'm merging onto a highway and accelerating quickly to 4k RPM and then let off the gas, there will be little to no vibration until it drops down to 1800 RPM or so, and then it's very noticeable until it hits 1600 RPM. I won't feel it again until I get back into that RPM range or come to a complete stop and feel it at idle. VCDS doesn't show anything, coolant and oil levels are where they should be so I'm not loosing any into the cylinders and causing it to run rough. This is a physical vibration that is felt, not heard.

I was thinking maaaaaybe it's the motor mounts, but there's no other pops or clunks, and the car still runs amazing. I took it to my mechanic for diag, and we got the car up on the lift, and started driving it. When I held it at 1800 RPM, they could actually feel the lift vibrating. Flex pipes were fine, trans mount was fine, driveshaft carrier was fine, and there was nothing visibly vibrating.

At this point the mechanic is also kind of leaning towards the motor mounts. But the engine barely moved when I power braked it, and he's a bit hesitant to throw parts at it, especially since you can't really inspect the mounts without basically doing the entire job. He was able to get a mirror in there and see a bit of the mount, but there was no fluid that we could see around them.

Car is EPL stage 2 single upper pulley, DSG tuned, CAI, gutted stock cats that had the welds reinforced, stock down pipes to a Gibson muffler feeding into Vibrant resonators, then into the stock mufflers out back. Anyone else ever experienced this, or have any ideas?

[BEight SFour]

Wheel bearings? Lug nut loose?

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[Lockon_B7]

If the motor mounts are bad enough to cause a vibration like that, if you take the belly pan off you'll likely see the purple hydraulic fluid leaking down from them.

[Audibot]

I'm with engine mounts. My C7 had a slight vibration which I thought was a wheel balance, but probably because it's diesel. Tuned engines can wreak havoc on original mounts. Mine was wrecked in less than 5k from going Stage 2.

[dizzysn]

Wheel bearings? Lug nut loose?

Wouldn't affect it at idle.

- - - Updated - - -

If the motor mounts are bad enough to cause a vibration like that, if you take the belly pan off you'll likely see the purple hydraulic fluid leaking down from them.

Belly pan was bone dry.

[Lockon_B7]

It wouldn't be as bad to leak down onto the belly pan, but it cold be seen on the motor mount brackets, the subframe and even the control arms in some cases.

[romanrnd]

I think I have the same issue, but haven't really looked into it. I was thinking it's flex pipes/cat/exhaust related. It seemed to have gotten worse when I gutted my cats. I would try throwing exhaust dampers on the downpipes and see if that helps. It could be motor mounts, but I just had my engine out and my mechanic said mine looked fine, but I know they can fail internally as well.

[ENV²]

Check motor mounts


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[hunter_killer]

Another member and I have the same problem too. I thought engine mounts by the way it vibrates with rpm, but mine are 034 street density and they aren’t leaking, nor have any play. I didn’t take a good look but I thought then either it’s the transmission bushings or exhaust causing the vibration. Only thing with the exhaust is it does it at idle too so would be a little weird getting a vibration like it does just idling. Idling it is a rhythmic pattern. My car is getting the timing chain covers resealed so I’ll see how things feel after the job is completed. Transmission is being pulled so we’ll check out the DMF for any oddities.


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[dizzysn]

Another member and I have the same problem too. I thought engine mounts by the way it vibrates with rpm, but mine are 034 street density and they aren’t leaking, nor have any play. I didn’t take a good look but I thought then either it’s the transmission bushings or exhaust causing the vibration. Only thing with the exhaust is it does it at idle too so would be a little weird getting a vibration like it does just idling. Idling it is a rhythmic pattern. My car is getting the timing chain covers resealed so I’ll see how things feel after the job is completed. Transmission is being pulled so we’ll check out the DMF for any oddities.


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I'd appreciate that.

And yeah I also have the rhythmic idle. It ALMOST sounds/feels like I've got aftermarket cams. I've gone over the plugs and coils and they're all perfect, and it's not misfiring.

At this point I'm almost convinced it's the exhaust. It's the same vibrations at the same RPM in every single gear, and it's the same intensity. If I'm at 1800 RPM and lightly accelerating, even just 1/10th throttle, it's fairly smooth, but let off and it's instant vibration felt throughout the car.

[hunter_killer]

I'd appreciate that.

And yeah I also have the rhythmic idle. It ALMOST sounds/feels like I've got aftermarket cams. I've gone over the plugs and coils and they're all perfect, and it's not misfiring.

At this point I'm almost convinced it's the exhaust. It's the same vibrations at the same RPM in every single gear, and it's the same intensity. If I'm at 1800 RPM and lightly accelerating, even just 1/10th throttle, it's fairly smooth, but let off and it's instant vibration felt throughout the car.

Yeah I’d say mine is the same, but it’ll really start bad around 2,200/2,100 rpm’s. I’ll for sure let you know how things are after I get my car back in the next week or so.


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[dizzysn]

Yeah I’d say mine is the same, but it’ll really start bad around 2,200/2,100 rpm’s. I’ll for sure let you know how things are after I get my car back in the next week or so.


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Mine has been almost "thumping" at 2,200 RPM during acceleration the last day or two, with this cold ass weather. It's almost like a really bad wheel balance. But it goes away when it warms up. I'm going nuts chasing this thing.

[hunter_killer]

Unfortunately I won’t be able to help out, yet, with this predicament. My oil leak is coming from my oil filter housing not timing covers so my transmission isn’t going to be removed. I am however going to be working on swapping my headers onto my car so I’ll be inspecting the cats and obviously replacing my flex pipes, so that may do some difference after all the work.


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[dizzysn]

Unfortunately I won’t be able to help out, yet, with this predicament. My oil leak is coming from my oil filter housing not timing covers so my transmission isn’t going to be removed. I am however going to be working on swapping my headers onto my car so I’ll be inspecting the cats and obviously replacing my flex pipes, so that may do some difference after all the work.


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All good, appreciate the update. At this point I'm thinking either down pipes or engine mounts. It's happening now in park, and the motor is almost completely still. I think that eliminates the trans, and since there's next to no movement on the engine itself, I'm not 100% on it being the motor mounts, though they're still on the list. I'm going to take it to an exhaust shop near by and have them look at the flex pipes/down pipes.

[mrg_B8TFSi]

If the motor mounts have been removed from the cause, I’m thinking it might be the intake balance shaft (or exhaust)? It’s possible that the balance shaft chain is stretched and/or maybe the shafts are out of sync with the cam chain? It’s a long shot but that vibration seems plausible.. have you done a full timing upgrade yet? And I don’t suspect that chain and shaft would throw any ECU faults


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[dizzysn]

Just to update this -

I haven't done ANYTHING yet. But about three weeks ago, it just stopped. Out of nowhere it completely stopped.

Drove the car and it was vibrating and pissing me off like it had been for months now, got home and parked the car. Came out the next morning to go to work, and the car was shaking a bit like it always does at idle. Hit 1800 RPM on my way to the stop sign, and it vibrated like it always did. Stopped at the stop sign, and there was no vibration. Continued on to work, and not a single vibration. It hasn't occurred since.

Someone just come burn my car down.