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P0171 code goes on/off on 1998 Buick LeSabre

I continue to have issues with a p0171 code showing lean, but it goes off and on. I would say it’s on 70% of the time and off 30% of the time.

I have hit it with carb cleaner pretty thoroughly and noticed no difference in idle. In general, it’s never a rough idle, either.

Any ideas? I got the vehicle in August with very low mileage of 37,500 miles and now it has about 44,000. Other things to note:
–At the last oil change, it obviously had incrementally lost oil but I have not noticed any leaks (nothing on driveway and oil pan gasket is not showing a leak).
–Before the p0171 popped, I took the Buick on the only long trip since I got it in August, going 225 miles a few days before Christmas and then 225 miles back about 5 days later. Otherwise, almost exclusively used for commute to work (18 miles each way, mostly interestate).
–Finally, I’m adding a photo of some gunk that is spitting out from somewhere and appears to be aimed at the passenger side axle boot. It’s built up pretty good.
–This all seems to me to add up to possibly the upper intake manifold gasket issue. I don’t mind taking a shot fixing that but obviously would prefer to be something less involved.

Replace the PCV valve, that might do the job on a car that isn’t driven very much. The PCV valve might be a little gummed up is all. Beyond that, in order of likelihood, you’re looking an air leak into the engine or exhaust system somewhere, a faulty MAP or MAF, or a faulty O2 sensor. Sometimes spraying ether in areas you suspect might be leaking air into the engine can provide a clue. If the rpm speeds up, you know the ether is finding its way into the engine, which it shouldn’t.

I agree with George. However, the Mass airflow sensor should be cleaned by removing it from the engine and using mass airflow sensor cleaner.( Reason is that it can be covered in dirt but still working) Very sensitive part, so don’t touch the working element.
The idle control solenoid could also be dirty. Disconnect it from the motor as well. and remove it for cleaning. Do not move the piston/ pintle valve. just clean the port opening. You’ll need Star Drive bits for the screws on both of these parts.
If there’s debris in that port, or the control itself is sticking, it’ll cause a lean condition.
The oil leak you showed could be as George said, It could be the intake gaskets. or the rear valve cover gasket. Possibly the front one too. But as I am dealing with that myself, I don’t suspect the front in your case.
In any event, the gasket set to do both sides is under $20. The rear bank may be a problem due to close quarters, so be methodical if you tackle it.
Also, there could be a cracked vacuum hose somewhere. Close inspection should reveal that.
You might want to check the Power Brake Booster for internal air leaks too.
Good luck, Your Buick should give you many comfy miles.

1 Like

Thanks so much. Appreciate the insights.

One additional observation: I am noticing that, once fuel is about 40%, the
code goes off. It then stays off until I fill up the tank, and comes back
on within the first 20 miles of driving after fillup. Then it stays on
until fuel tank drops below 40%. This pattern is now pretty consistent.

Certain tests the engine computer does for making sure the emissions system is working sort of follows that same scenario, when/if the test is done is affected by the gas tank fill level. Well, maybe it is just doing what it is supposed to be doing. But given the relationship to the fuel tank fill level, there could be an involvement with some failure in the evap system. Might be a good idea to give all that a visual inspection at least. Purge valves are a pretty common failure item reported here, not necessarily on 'Buicks, but in general. So if you are itching to replace something, might be worth a try. Better use of your time and money tho to have a proper diagnosis done first, they’ll tell you what’s wrong, then if you like you can do the component replacement yourself.

Much appreciated. I probably need to give in and ask someone to diagnose
because I do not have the equipment for testing but willing to DIY if I
know the issue.

Just wanting to raise this up again. Here are the pertinent facts about
this Buick LeSabre 1998 Limited – which I got in August with 38,000 miles
and now has about 45,000. I am new to DIY on vehicles and bought this in
part because I want to learn and willing to try with so little invested
(paid $2,400 for it).

  1. For about the last 2,000 miles, ever since the only extended trip I have
    taken (250 miles each way over Christmas), the p0171 code showing lean bank
    2 comes on and off – 65% of the time on, 35% off. It always comes on
    within 5-10 miles of filling up the tank. It almost always disappears at
    about a 60%empty/40%full.

  2. Last oil change, it was clear that oil is being lost somewhere but NOT
    from the gasket or drain pan. Seems to be in internal leak. Absolutely no
    oil drips onto driveway, parking lot, etc. So it must be leaking very
    lightly internally while engine is running and in motion.

  3. Recently, the CHANGE OIL SOON light has come on and stayed on –
    according to the manual, the computer does detect when oil has degraded.
    Although it was not the CHECK OIL LEVEL light, I did see was almost a quart
    low and so I have topped it off.

  4. While I believe this could be the intake manifold gasket issue, I have
    sprayed and sprayed with carb cleaner and noticed no difference in rpms. In
    general, the car does not idle roughly – seems very normal to me. No real
    issues at all, in terms of noticeable symptoms.

Appreciate any further thoughts on this. My other issue is that
relationship with very trustworthy regular mechanic for years has been very
much – “you just do whatever it takes”. So while certainly it’s possible
for me to adjust the relationship to “diagnose for me and i’ll fix it
myself,” his is not the type of shop where that’s customary.


First of all the shop will want to charge for this diagnosis and they should. Second if I had a shop I would tell you that I would not diagnose without also doing repair just in case I was wrong and it did turn out to need more than first thought.