Dodge Repair: Brakes and rough running engine, air filter oil, rear cylinders

Question
I bought a 92 dakota from an auction, big mistake.  The engine runs very rough and have used 3/4 of a tank of gas for 90 miles.  The brakes are really bad.  They will work but the whole front end shakes when I use them.  My boyfriend replaced the booster, master cylinder, rear cylinders and all pads.  He has now given up on them.
The engine has gotten new plugs, wires, pcv filters, air filter, oil and filter.  The check engine light is not on so a diagnostic test would not help.
I am a single income family and do not make very much money.
Any insight would be appreciated.

Thank you for your time

Answer
Hello christine
the brakes sound like bad rotors did he change the rotors this would make the front end shake .

now as far as motor this could be a vac line off from fuel engt. or it could be a bad o2 senser.

have your boy frend check all bolts on fuel engt . also could be sucking air . good luck to you hun and if you need more help let me know and you have a pretty name pete