P0171 to lean high idle

[jeffro312]

So every once in a while I get this code p0171 as soon as light comes in engine idle revs to 950-1000 if I clear code in torque engine idle drops instantly to normal 600 or so.


I though vacuum leak checked around. The cap on the plastic intake manifold box thing as cracked replaced it and hose from fuel pressure regulator cracked replaced it

Still it pops up. Sometimes I get the high idle with no code etc.

Nothing I do reproduces it nothing else seems different besides harder to stop due to high idle.

Any suggestions Thanks In Advance

 

[IllogicTC]

Perhaps looking into your SAIS system. Plenty of threads about the secondary air injection system. A failed valve may allow exhaust to go backwards through the system, or perhaps there may be a venturi effect where it would pull fresh air through the system into the exhaust which would make it read lean.

Also ensure that the bolts for both manifolds are to tightened to spec.

You have Torque so you should be able to graph O2 sensor performance, right? Getting us a graph would help if you can do that. Simple observation may provide some clues.

And what year, how many miles?

 

[jeffro312]

04 212000 miles. Will get 02 readings as soon as I get a new elm bluetooth reader mine shit the bed stopped working today

Will research sais on thing on my truck haven't messed with yet thanks for reply

 

[thisguy1985]

also check you fuel pressure, it should be around 50psi. I just had the same problem, i started checking and replacing(if needed) everything that could cause the p0171, nothing was working untill i read that low fuel pressure can cause it. i checked mine it only had 25psi, so i replaced the fuel pump and its running great now

 

[jeffro312]

also check you fuel pressure, it should be around 50psi. I just had the same problem, i started checking and replacing(if needed) everything that could cause the p0171, nothing was working untill i read that low fuel pressure can cause it. i checked mine it only had 25psi, so i replaced the fuel pump and its running great now

Where is the port to trest fuel pressure?
And how hard was it to change fuel pump

Thanks for info. I'm still waiting for elm Bluetooth obd2 dongle in mail so going to wait for that and check fuel pressure

 

[Mounce]

For your year model it should be right by the fuel filter which will be under the driver side mounted to the frame. A member here, MAY03LT, has a great video explaining how to check the pressure and if I remember right, he shows how to do it also.

 

[Mounce]

Here's a link to his video.

Chevy Trailblazer - testing fuel pressure: http://youtu.be/sGDG4LkdzFU