A few weeks ago I bought a 2003 Buick LeSabre for a remarkably cheap price given its value+condition (supposedly it wasn’t the owner’s car, it was his mother-in-law’s who had passed and he just needed it gone.) I figured there might’ve been some “catch” he didn’t mention, but generally it ran beautifully when I got it, but there are two issues that worry me slightly.

First of all, the gas gauge seems to fluctuate a large amount. Most of the time it’s not major, but the most extreme difference happens whenever I put it into park, the gauge immediately drops significantly. It “jumps” up and down a few times until resting at a much lower level, usually almost half the capacity lower than it was before. When I start driving the gauge raises again, and it gets at its highest after going on the freeway. It drops a little bit when I’m at a stop light, but it’s never as immediate or as much as when I put it into park. I wouldn’t be too bothered by this except for the fact that I can’t tell which level is more accurate. I can’t tell if the tank is halfway full when it says halfway when driving, but nearly empty when parked, and since I drive delivery for several hours a day I absolutely don’t want to end up out of gas because I thought there was more. I’ve been going off the parked reading just to be safe, but it would be nice to know if it is the driving reading so I can have some peace of mind—especially if I want to go on a road trip or visit another city with it where I’ll be on the highway continuously for several hours.

The second issue wasn’t there when I bought the car, it only started happening about a week ago. When I try to put in gas, the pump immediately clicks off due to resistance as if ti was full, even though it absolutely isn’t full (this can’t just be a gauge accuracy thing, it doesn’t leak and it happened even after refuelling haven driven 33 miles the night before). The only way I could fill up the tank is to barely pull the trigger down at all and let it drip in extremely slowly. Yesterday when I filled up, I had the same problem but I was able to use muscle to really shove the pump into the tank and from there it let me pull the trigger down all the way just fine, but I haven’t tried filling up since then so I don’t know if that was a one-time solution. Another poster on here had the same problem with their LeSabre and said it was likely a clogged EVAP system—assuming the problem didn’t go away after yesterday, is that dangerous to drive? If I have to continue forcing the pump in or slowly, is that going to be bad for the car?

Could these problems be related? How difficult/expensive would they be to fix? Would appreciate any advice, I only got my license this year and I’ve learned a bit about cars in that time but I couldn’t be farther from an expert.