Low Idle, and intermittent misfire

[Prerun4fun13]

Ok so I have a:
94 ford explorer
4.0 Automatic trans, 4x4

I have a low idle (right around 500-600ish) and an intermittent miss that usually happens while I'm driving but will also happen sometimes at idle. I am coming up with codes 121, 522, 566, and 421 (i can't find anything on that one so I'm thinking i might have miscounted the blinking lights)
So parts I have replaced trying to fix the problem are as follows
MAF
Coil Pack
fuel filter
newish plugs (gonna change those this weekend)
and newish wires

The 121 code is "throttle position sensor out of test range"
Should I try replacing the TPS or is there something else related with this code that could cause this issue? Also what is the deal with the transmission codes? The tranny seems fine but it runs like crap.
Thanks again for any advice/ input. I am about to start banging my head against the wall with this truck.

 

[acschilling]

The TPS COULD be out of range. A good DMM will cost you the same as a new TPS. I had the same suspicions recently on my 92 5 speed but my TPS tested near perfect even with mismatched screws. Is your CEL on or are these like stored codes? Does this miss cause a slight bucking or jerk while driving?

Hope you didn't get crap replacements from the store.