IMO you should START with the P0103 following by the P1121. They may even have a common cause. Think wiring or dirty connectors first.
Do you have an ODB2 scanner? If you did it might make short work of this problem. Use an ODB2 to monitor the MAF signal as well as the TPS voltage.
Is there ANY moisture on top of the motor? On the 4.6 SOHC the spark plug holes are straight up and down. IF there is any water on top of the motor it will migrate down the spark plug holes and CAUSE a misfire.
Note, if a moisture related misfire is allowed to continue it will damage the COP insulator. Once damaged the misfire will continue even after the moisture has been corrected. In these cases consider replacing just the COP boot insulators. A complete set of ( 8 ) is cheaper than a single replacement COP.
While working on your car have you ever wanted: to find an ODB2 operational PID value (say fuel pressure or MAF)? How about graph a PID value over time? Or compare multiple PID's over time? Access a bi-directional PCM control such as test a...
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P0103 - Mass Air Flow (MAF) Circuit High Input
The MAF sensor circuit is monitored by the PCM for high air flow (or voltage) input through the comprehensive component monitor (CCM). If during key ON engine OFF or key ON engine running the air flow (or voltage) changes above a maximum calibrated limit, the test fails.
MAF sensor screen is blocked
MAF circuit shorted to VPWR
Damaged MAF sensor
Damaged PCM
A MAF V PID (MAF PID) reading less than 4.6 volts (Refer to equivalent grams/second chart in GO to Pinpoint Test DC ) in continuous memory or key ON and engine running indicates a hard fault.