99 Ford Contour shakes

Among other issues … I have a 99 Ford Contour that sporadically refuses to start. The engine will turn over (is that the right term?), but it won’t “catch,” for lack of a better way to put it. It seems to happen more frequently when the gas gauge is at 1/4 of a tank or below. A dealership told me it was the fuel pump and quoted $985 for the repair (more than the car is worth), but a second opinion from an independent garage says it might not be the fuel pump. (Though they don’t know what is causing the issue because, of course, it never behaves the same when the mechanic drives it). The second issue, which may or may not be related, is the vibration in the car. It happens only if I turn on the AC or heat. And I do mean shake - it’s very noticeable and loud. The motor mount has been checked and that’s not the issue. I’m a student & this car needs to last me another year so I can get out of school and (I hope) get a good job. Any ideas/suggestions are welcome. Thanks.

How is a shake “loud”? Is there a sound accompanying the shake, such as a rattle? It would be helpful to know the type of sounds we are dealing with. Many cars will have a lower idle speed with the A/C or certain heat settings engaged. This is normal and may cause some additional vibration (due to lower idle speeds). What is not normal is to have additional noise occur. This can be caused by loose heat shields, bad motor mounts, or other items on the car that are no longer secure. You will get more useful responses with a more complete description of the problem, in this case the sound that is being generated.