Long term fuel trims lean
Thread Starter
Teching In
Joined: Jul 2012
Posts: 29
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Long term fuel trims lean So I was driving today and the trouble code p0171 showed up. I checked my fuel trims and they are maxed out to +25.
These are my diagnosing steps:
Vacuum Line Leaks
Intake Leaks
Clogged Fuel Filter
Any other suggestions would be appreciated.
One thing I do have a question about is when the car is idling and I have the hood open you can easily hear an audible sucking noise? Is this normal and I'm just hearing air going through the throttle body, or is this the possible vacuum leak?
These are my diagnosing steps:
Vacuum Line Leaks
Intake Leaks
Clogged Fuel Filter
Any other suggestions would be appreciated.
One thing I do have a question about is when the car is idling and I have the hood open you can easily hear an audible sucking noise? Is this normal and I'm just hearing air going through the throttle body, or is this the possible vacuum leak?
If the sound seems to be coming from the throttle body it could be coming from the back of the small rubber piece on the passenger side of the throttle body neck. It goes to the pcv valve. Stick your finger on the back of it. It is usually pretty obvious. You can also spray some starting fluid around the intake and areas of possible leak. The engine will choke a little or rev a little when you get around it. Obviously the engine will need to be idling when sprayed.
Thread Starter
Teching In
Joined: Jul 2012
Posts: 29
Likes: 0
If the sound seems to be coming from the throttle body it could be coming from the back of the small rubber piece on the passenger side of the throttle body neck. It goes to the pcv valve. Stick your finger on the back of it. It is usually pretty obvious. You can also spray some starting fluid around the intake and areas of possible leak. The engine will choke a little or rev a little when you get around it. Obviously the engine will need to be idling when sprayed.
The rest of the line was dry rotted and cracked, so I guess I will have to make a new pcv system. I plugged the vacuum port; the idle dropped and the sucking sound went away. I didn't have time to hookup the computer, but I am hoping it was this simple fix.
**Update**
It was the pcv hack job causing the issues. As soon as I stopped the vacuum leak the short term fuel trims dropped right down to zero and the idle went from 850-900 to 750-800 obviously much smoother too.
Last edited by gak68; May 23, 2014 at 10:18 PM.
