C6 running rough
Thread Starter
Intermediate
Joined: Aug 2023
Posts: 33
Likes: 1
C6 running rough
2008 a6 w/ 42000 miles
Hasn’t been pleasant driving my c6 for the past months. Here’s some reasons:
When pressing on the gas at slow speeds, I hear like air is getting sucked in. Already had a shop do a vacuum leak test and didn’t find nothing. I also checked my fuel trim and everything was good.
When in traffic, if I gentle press on the gas, the car “bucks” or if like someone just hit me from the back. Can it be something with my exhaust ? I just passed smog like 2 months ago. Or can it be the air to fuel ratio?
Can it be due to the fact Ive been filling up my gas tank for only half way because of the gas tank leaks due to the cheap plastic. It’s a 2k plus job.
The car is not throwing any codes, some shops even said if it’s not throwing a code the car is fine, which is them just being lazy.
Anyone had similar problems?
Hasn’t been pleasant driving my c6 for the past months. Here’s some reasons:
When pressing on the gas at slow speeds, I hear like air is getting sucked in. Already had a shop do a vacuum leak test and didn’t find nothing. I also checked my fuel trim and everything was good.
When in traffic, if I gentle press on the gas, the car “bucks” or if like someone just hit me from the back. Can it be something with my exhaust ? I just passed smog like 2 months ago. Or can it be the air to fuel ratio?
Can it be due to the fact Ive been filling up my gas tank for only half way because of the gas tank leaks due to the cheap plastic. It’s a 2k plus job.
The car is not throwing any codes, some shops even said if it’s not throwing a code the car is fine, which is them just being lazy.
Anyone had similar problems?
Instructor
Joined: Sep 2018
Posts: 211
Likes: 79
From: Sparks NV
I am no expert but just throwing this out there it sounds like a signal being lost between the pedal and the throttle body then when you pass the bad spot it jumps open the throttle body and give a lurch to the car. When sitting out of gear and slowly raising the rpm is there any flat spots on the rpm gain?
Melting Slicks
Joined: Apr 2019
Posts: 2,500
Likes: 1,165
From: Northern Wisconsin
When pressing on the gas at slow speeds, I hear like air is getting sucked in.
If you have something as obvious as this, I would start by pinning down the location of the sound. You might need a helper with this. Maybe someone listens to the engine bay while another person presses on the gas with the car in gear and brake on.
If you have something as obvious as this, I would start by pinning down the location of the sound. You might need a helper with this. Maybe someone listens to the engine bay while another person presses on the gas with the car in gear and brake on.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,564
Likes: 4,034
From: Cape Coral, Florida
Yes, first figure out what may be leaking…since you have a scan tool what are your long and short term fuel trims at idle…with ignition on first let us know what your MAP sensor reads…if your scan tool shows Kilo Pascals see if it reads around 103 or if your scan tool shows Baro it should read 29.2 inches mercury at sea level…if fuel trims are plus or minus 10% at idle what do they read under load up to the 1-2 shift ??…also look at your front O2 sensors…they should go full rich from 900-1000mv’s under load….if your scan tool can graph and you can record it that’s makes it much easier…if fuel trims increase under load you have a MAF issue or fuel delivery…as far as air/fuel ratio if your scan tool shows “Lamda” you should see 1.00 is ratio is good…your tank concern has nothing to do with your concern…99 out of 100 shops or dealerships are CLUELESS when it comes to diagnosing drive ability issues…they only know how to change parts…diagnostics requires a completely different skill set…your shop mechanics are “witch doctors” and a diagnostician is a Harvard trained doctor… this is the only way I can easily explain this…BTW if you had a vacuum leak your fuel trims will be elevated…also at hot idle your MAF should be reading from 6.2 grams/second to 7.0.
Last edited by C5 Diag; Jul 30, 2024 at 06:18 PM.
Thread Starter
Intermediate
Joined: Aug 2023
Posts: 33
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Yes, first figure out what may be leaking…since you have a scan tool what are your long and short term fuel trims at idle…with ignition on first let us know what your MAP sensor reads…if your scan tool shows Kilo Pascals see if it reads around 103 or if your scan tool shows Baro it should read 29.2 inches mercury at sea level…if fuel trims are plus or minus 10% at idle what do they read under load up to the 1-2 shift ??…also look at your front O2 sensors…they should go full rich from 900-1000mv’s under load….if your scan tool can graph and you can record it that’s makes it much easier…if fuel trims increase under load you have a MAF issue or fuel delivery…as far as air/fuel ratio if your scan tool shows “Lamda” you should see 1.00 is ratio is good…your tank concern has nothing to do with your concern…99 out of 100 shops or dealerships are CLUELESS when it comes to diagnosing drive ability issues…they only know how to change parts…diagnostics requires a completely different skill set…your shop mechanics are “witch doctors” and a diagnostician is a Harvard trained doctor… this is the only way I can easily explain this…BTW if you had a vacuum leak your fuel trims will be elevated.
Last edited by Ed1801; Jul 30, 2024 at 06:23 PM.
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
Thread Starter
Intermediate
Joined: Aug 2023
Posts: 33
Likes: 1
sorry about the audio
Thread Starter
Intermediate
Joined: Aug 2023
Posts: 33
Likes: 1
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Brett Foote
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
If this is a WOT pull 130 grams/second looks OK…I think you should find a professional diagnostician in your area and let him determine what’s wrong with your car since you have no DTC’s…I really don’t need the audio…having a scan tool where you can graph 6-8 data PIDS and record them is preferred over looking at just 2-3.