Need advice: CEL P0171

[zdkaiser]

Hello,

Last night my check engine light came on during my drive home from work (it was 1 degree F at the time; I live in Montana). I have a 2007 base vibe with ~90K miles on it.

The code was on again this morning when I started it up. I went into town (~15 mile drive) and filled it up with gas and the CEL turned off when I restarted the car after fueling up.

I had the code read shortly after I got gas this morning at the GM dealer and the mechanic said is was "Running too lean" P0171.

I then drove it home 15 miles and the CEL light still didn't come back on.

I was wondering if:

A. Could a loose gas cap throw a P0171? (I do drive my Vibe up and down gravel roads a lot, so I thought maybe it jarred itself loose).

or

B. Could it be the faulty gasket on the manifold? Should I replace it?

I replaced the front 02 sensor last year, so that should not be the issue.

Otherwise the only other symptoms I have noticed with the car that seemed slightly odd was, yesterday after the car was fully warmed up, it hickuped 3 times when I was going 60-65mph. It did not do this again, nor was the CEL light on at this time. Also, about a week ago before the hiccup event, it was -10 or so, and the engine was sputtering at idle when it was partially warmed up. It was going from about 500rpms to about 1000 rpms. This is the only time it did that. I thought maybe it was cold related.

Other than those 2 brief occurences, it has been running well. I got 28.8 mpg on my last tank. I just replaced the engine oil with Mobile 1 full synthetic (and the oil is full). I also did 2 drain and fills on the tranny fluid with TIV. Those levels are good as well.

I am looking for advice on the fix for the time being, but I may ride it out a little while longer and see if the CEL comes back on.

[zdkaiser]

Any advice on where to look for vacuum leaks under the hood?

Or how to test for leaks in the manifold gasket?

I have some carb cleaner I could spray around the manifold and listen for the increased idle. Would this work?

Also, will carb cleaner damage plastic?

[Raven]

PO171 is quite common apparently. Intake manifold gasket is the likely culprit. Vibe's run on the rich side anyways. I've had this code for well over 2 years. Carb cleaner should show the problem. You could use Quikstart (ether) also.

[Salsa Guy]

Normally that year doesn't have problems with the intake gasket. More than likely is some type of vac leak. I don't recommend ignoring the issue like Raven because he makes the assumption that these engines run rich. I had a wideband sensor my car and can tell you they may running a little rich but the code doesn't tell you how lean. Running Lean can cause the engine to have ugly failures, burning valves, knocking holes in pistons and nasty issues.

[lannvouivre]

Normally that year doesn't have problems with the intake gasket.

Mine is an '06 base; I replaced the gasket sometime last year and it almost came off in pieces. You may consider pulling the intake manifold and inspecting the gasket to see if it's rubbery or hardened to plastic; it's not too bad of a job.

Seconding Salsa's advice on running lean dangers.

[cptnsolo77]

Dont rule out the gas cap. The Vibe threw that code about a year ago for me. I disconnected the battery & I made sure I clicked the gas cap 3 times after I fill up. havent seen the code since.

[zdkaiser]

Thanks for the responses.

I am not too sure if it was the gas cap, because from what I have read a loose cap shouldn't throw a P0171 code. Although, after I filled the tank and reclicked the cap a few times the light turned off. I don't know if that was just a coincidence or not.

Anyways, I ordered the new gasket online for $4 plus shipped (no big expense), and I am going to wait and see if the CEL comes back on. If it does, I will probably swap it out once it get fairly warm out (no garage).