Chasing persistant p0171 code 2009 1.8l

[jack2009]

Hello All,
Iam pulling my hair out over this issue. My daughters 2009 1.8l vibe keeps throwing p0171 codes. It got worse over the past cold weeks in the mountains of NC. I have replaced the intake manifold and throttle gaskes with no luck. The car will ide ok, but usung the odb2 reader I notice that the air fule ration sometimes will creep up to 17.5 air to fule and the idle roughens a bit. As expected. I have searched for the usual vacume leaks and I have not found any. I have spraded a bit fo carb cleaner around the various sea, hoses and clamps and nothing really happenend. One odd thing I did notice is that if I pull up on the bottom of the intake manfold the air fule ratio slowly moved to lean nd if I pushed down the readings richened up. OK, so I might have a clue. I next lostened the bolt on the bottom of the intake manifold and then retightend it and the readings held.

I like good news but I am afraid that the issue will just show up again.
Does any one have a better suggestion on what is going on? Do I need a new intake manifold? have people been having problems with them?

I appreciate any help I can get and will share the solution once it is discovered.

[lannvouivre]

What if you just use some RTV gasket in addition to the rubber one? Make sure you're only snugging it down, not wrenching the heck out of the bolts/nuts, as well. Please take no offense if that seems obvious, it's just a common problem (over-tightening).

[jack2009]

The issue is not fixed. Driving in this morning I saw the idle A/F ratio go up to 17.5 at a stop light. I did not jump but slowly crept up over 20-30 seconds.

Could a PVC valve do this? I have not found a nice clear explanation of how they work. I know that blow by gasses are sucked back into the intake to avoid polluting the world, but I read that the vale has a spring in it to prevent it from dumping blow by during Idle. Could have mis read that one.

Any way, i am going to try something I saw in a post, use a propane torch to supply gas via a hose and see where the engine A/F ratio changes when I get the gas near a leak, if there is one and I am not chasing the wrong issue.

Any way, thanks for the idea. It is on my list.

[vibrologist]

There is one place that gets routinely missed: the oil cap. The cap needs to be seal, or air enters and goes through the PCV valve. Make sure the grommets around the PCV valve are seal and pliable.

Also the way you describe it it is a small leak and that's why you have trouble finding it. Be patient, don't give up.

[circuitsmith]

Make sure there are no air leaks between the throttle body and the MAF sensor.

[jack2009]

OK I finally figured it out. Basically, the intake manifold had hair line crack about 2/3rds around the lower mounting bracketon the lower right side of the intake manifold. This was not the attachment points on the head, but down low beneith the throttle body on the engine block. The crack was around where the mounting leg attached to the intake manifold. I took the manifold off and roughed up the area around the lower mounting bracket and used some JB weld epoxie around the cracked area. This fixed the problem so far,about 1000 miles.
I have also figured out how to take the manifold off in about 15 minutes. Hope this helps the next person.
Oh I used some carb cleaner and flooded various areas until I finally got a reaction from the engine and the fule trim moved about.