Follow-up to my follow-up:

I tried to solder the wire back into the connector for the EGR sensor. It
wouldn't take so I just went ahead and disconnected the sensor altogether
and the car seems to be running better. Are there any dangers or risk to
disconnecting the EGR?

What do motor mounts have to do with the engine's wiring harness?

A damaged wiring harness must be replaced:

it won't fix itself,

its unreliability makes the car dangerous to drive,

the constant aggravation will drive you nuts,

the car can't be sold this way - even if you bought it so.

The pain can be lessened by installing the new harness yourself -
tedious, dirty and time consuming but no physically hard wrench pulling.

MB, stop thinking the mechanic is dishonest for IMHO you are being
dishonest, with yourself - about the lousy car that YOU bought!
Remember, nobody forced you to buy THIS car. You thought it was a
bargain - that's the worst kind of luxury car to buy, there are no bargains.
One pays up front for quality or later for having bought crap, but in
either case one pays!

That sounds kind of drastic, just to deal with a broken wire going
to a specific component.  Reminds me of the usual dealership approach
to soaking customers: "While we're replacing that light bulb, we
might as well replace the alternator, the voltage regulator and the
wiring harness, just to make sure.  You wouldn't want your wife and
kids to be stranded someplace, would you?"

Why not just splice in a new length of wire?  Seems to me the
splice could be adequately weatherproofed with a coating of
grease inside some shrink tubing.  Badda-bing, badda-boom;
on the road agin' in no time.

Geoff