Fluctuating revs

Tiny
JAY JACKSON
  • MEMBER
  • 2007 AUDI S5
  • 4.2L
  • V8
  • 4WD
  • MANUAL
  • 83,000 MILES
When the engine is cold it drives faultless but as the engine gets warm is where the niggles start showing. When pulling away the revs fluctuate up and down quite rapidly. Then when driving the car jerks in first and second at high revs. It's a manual transmission.I have had spark plugs changed, fuel filter and had it terra cleaned but still no change. Any advice would be greatly appreciated. Many thanks.
Monday, March 18th, 2019 AT 3:38 PM

11 Replies

Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey JAY JACKSON,

Is the check engine light on?

Do you have access to a code reader? If you can provide a list of the current fault codes we can narrow down the potential causes.

Regards, Joe
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Tuesday, March 19th, 2019 AT 11:53 AM
Tiny
JAY JACKSON
  • MEMBER
  • 6 POSTS
Hi Joe,

No there are no warning lights and no fault codes.
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Tuesday, March 19th, 2019 AT 1:39 PM
Tiny
JOETECHPRO
  • MECHANIC
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Hey JAY JACKSON,

From having a search i have found a few people having issues with leaking motor mounts on these vehicles.

I found a good video, it shows around half way through where to check for leaks from the mounts.

It also has a method of check for vibration that may/ may not be useful i would definitely recommend checking for leaking mounts though.

https://www.youtube.com/watch?v=bofw2MYc0zE

Without having fault codes it may be difficult to track down the cause of your fault but at least this is an easy visual check.

Hope that helps,

Regards, Joe
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Tuesday, March 19th, 2019 AT 5:52 PM
Tiny
JAY JACKSON
  • MEMBER
  • 6 POSTS
Thanks Joe, I will take a look at this. I have ordered a code reader to so will also once again check myself for any codes. Many thanks again.
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Wednesday, March 20th, 2019 AT 12:01 AM
Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey JAY JACKSON,

No problem, keep us updated on your progress.

Regards, Joe
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Wednesday, March 20th, 2019 AT 11:19 AM
Tiny
JAY JACKSON
  • MEMBER
  • 6 POSTS
Hi Joe, I purchased a code reader and it is saying that both engine mounts need changing, so I think you are spot on.
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Wednesday, March 20th, 2019 AT 11:36 AM
Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey JAY JACKSON,

Have you checked for leaks at the mounts?

What codes have you got stored?

Regards, Joe
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Wednesday, March 20th, 2019 AT 11:57 AM
Tiny
JAY JACKSON
  • MEMBER
  • 6 POSTS
Hi Joe, did a scan and this is what came up.
Images (Click to make bigger)
Thumb
Thumb
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Friday, March 22nd, 2019 AT 7:34 AM
Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey JAY JACKSON,

I would say still check the engine mounts for leaks and replace if leaking.

It looks like the solenoid is part of the mount.

There will be an electrical connector on the top of the mount, If you don't find any leaks ensure these connections are plugged in correctly.

From what I can see the motor mounts going bad is fairly common.

You could also look into replacing the mounts with a solid non fluid filled mount, the fluid filled solenoid mounts may be quite expensive.

Hope this helps, let me know if you have any further questions.

Regards, Joe
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Saturday, March 23rd, 2019 AT 10:14 AM
Tiny
JAY JACKSON
  • MEMBER
  • 6 POSTS
So I have had engine mounts changed, throttle body cleaned out and mechanic look at it and still no luck. He told me just to keep driving it until engine light comes on. Anyone have any ideas?

When I first switch on the engine and the revs are slightly higher as the car is cold everything seems to be okay. It is when the revs drop to normal is when issues start. I have tried pulling away using only the clutch, when I do this all is good with the revs. When you introduce the accelerator then there's problems. I have also noticed that when pressing the accelerator at idle the needle surges up, you can't seem to gradually get the needle to climb. And not sure if this is me but when I go to change gear the car really pulls back.
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Saturday, November 9th, 2019 AT 12:30 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
How long have you been driving the car? It needs to be driven long enough to set a code or pending code so we can see where to look first. You could have a vacuum leak. here is a guide to help you confirm:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please run down this guide and report back.

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Tuesday, November 12th, 2019 AT 10:48 AM

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