2000 Ford Expedition idle problem?!

This car has been sitting for about 5-7 months before finally using it in September/November of 2015. This car was used to jumpstart another vehicle but the guy who connected the wires did it improperly and his car died too. The car wouldn't start, Triple A said it was the fuel pump not getting fuel to the engine. They banged on the fuel pump and jump started and it worked well and fine. Up until recently, I've noticed while braking/coming to a stop the idle would drop around from 500 to 300 RPM, shake, and the idle would come back up. I cleaned the MAF and the throttle body ( did not remove throttle body, cleaned it while still attached. ) and I took the car for a test drive, but then the car would hesitate now. While driving, the car just stays at 1,100 rpm even with gas. The RPM drops at times but not too low anymore and drops to 500 most of the time. Took it to a mechanic and they changed the IAC and oxygen sensor but that's about it. The problem still remained and upon cleaning the MAF and throttle body, now the car hesitates or stays locked at a certain rpm and idle drops at coming to a stop. No codes except for a P0113 and went away upon checking the sensor. The car would occasionally make a cranking/grinding noise but not start and it would STSRT on the second try.

Assumptions:
- Fuses? Because of that failure to connect jump cables correctly
- Fuel pump or filter?
- Spark plugs?

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