p0171 code off and on LeSabre 1998

[1998lesabre]

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.

 

[HotZ28]

Some good info on P0171 - https://youtu.be/3RFTS22w6tM

Are yo sure the CV boot is not cracked & leaking. That cross-member looks like it is covered in grease. Take a sample of the gunk with your fingers and see if it is greasy.

 

[1998lesabre]

One additional observation on the p0171 code: 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.

Thanks for the observation on the CV Boot. Any tips on remedy? I'm not sensing any problems with that axle -- no bad noises on turns, etc.