Quick PCV Question
Thread Starter
Racer
Joined: Oct 2010
Posts: 278
Likes: 1
From: Ware Shoals SC
Quick PCV Question
I've had fluctuating idle and choking conditions in my '99 A4. I found a bad vacuum leak in the short hose from the pcv valve to the intake just behind the throttle body. I replaced the pcv valve and leaking hose today. I'm hoping this will fix the lean codes I get from time to time. The irratic idle has stopped but the car still wants to choke in reverse.
My question is: Does it take a while for the computer to re-adjust from the lean running environment it has been dealing with for a few weeks?
I have only driven it about 5 miles since fixing the leak. Thanks for any advice. I hope I don't have to trace another leak somewhere.
My question is: Does it take a while for the computer to re-adjust from the lean running environment it has been dealing with for a few weeks?
I have only driven it about 5 miles since fixing the leak. Thanks for any advice. I hope I don't have to trace another leak somewhere.
Melting Slicks
Joined: May 2008
Posts: 2,606
Likes: 355
From: Rochester New York
I've had fluctuating idle and choking conditions in my '99 A4. I found a bad vacuum leak in the short hose from the pcv valve to the intake just behind the throttle body. I replaced the pcv valve and leaking hose today. I'm hoping this will fix the lean codes I get from time to time. The irratic idle has stopped but the car still wants to choke in reverse.
My question is: Does it take a while for the computer to re-adjust from the lean running environment it has been dealing with for a few weeks?
I have only driven it about 5 miles since fixing the leak. Thanks for any advice. I hope I don't have to trace another leak somewhere.
My question is: Does it take a while for the computer to re-adjust from the lean running environment it has been dealing with for a few weeks?
I have only driven it about 5 miles since fixing the leak. Thanks for any advice. I hope I don't have to trace another leak somewhere.
Disconnecting the battery should reset your fuel trims, it takes a good amount of driving for all the fuel trims to relearn. After a good 100 or so miles, check the long term fuel trims with a scan tool. If you average +20% or higher I'd say you still have an intake leak. +25% triggers the lean code.
Thread Starter
Racer
Joined: Oct 2010
Posts: 278
Likes: 1
From: Ware Shoals SC
Thanks for the advice man!
The leak was in the "elbow" tube. The 2" tube between the pcv valve and the plenum box behind the throttle body up front. The oil vapors (I need a catch can) over the years turned the tube into soft goop and it had formed a pretty big hole in the bottom of it. I will disconnect the battery and put some miles on it and then grab the laptop and log a drive with autotap and see where my trim banks are. Your advice was just what I needed.
The leak was in the "elbow" tube. The 2" tube between the pcv valve and the plenum box behind the throttle body up front. The oil vapors (I need a catch can) over the years turned the tube into soft goop and it had formed a pretty big hole in the bottom of it. I will disconnect the battery and put some miles on it and then grab the laptop and log a drive with autotap and see where my trim banks are. Your advice was just what I needed.
Race Director
Joined: Feb 2008
Posts: 17,336
Likes: 8
From: Maker of Sharp Objects, AL - Roll Tide
St. Jude Donor '10-'11-'12-'13-'14-'15-'16-'17
St. Jude Knife Maker
Had the same symptoms you were describing in mine. My air/vacuum leak was so bad that it sounded like someone holding an air hose under the hood. Finally, the other day I got to the point where I had enough, and I found the leak. It wasn't hard to find because the leak was so bad. I have just been putting it off for some time.
If you look right in the center of the pic you can see the hole in the hose. I'm not sure if this is the same place that yours was or not.
If you look right in the center of the pic you can see the hole in the hose. I'm not sure if this is the same place that yours was or not.
Thread Starter
Racer
Joined: Oct 2010
Posts: 278
Likes: 1
From: Ware Shoals SC
Had the same symptoms you were describing in mine. My air/vacuum leak was so bad that it sounded like someone holding an air hose under the hood. Finally, the other day I got to the point where I had enough, and I found the leak. It wasn't hard to find because the leak was so bad. I have just been putting it off for some time.
If you look right in the center of the pic you can see the hole in the hose. I'm not sure if this is the same place that yours was or not.
If you look right in the center of the pic you can see the hole in the hose. I'm not sure if this is the same place that yours was or not.
Can a vacuum leak like that make it so lean it will eventually burn a piston? Mine may have been that way for quite a while. I would think I would have constant lean code before it burned a hole through a piston on an LS1. These ain't Harley Davidsons.
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