1997 Nissan P/U turns over but wont start

My mom's truck (1997 Nissan / 2400 12 valve) has been having some problems & I had it towed over to my place to fix it. I fixed it previously from running like garbage & she drove it at least 500 miles with no problems. Then last week she started it, started to pull out of the drive and heard a feint "pop" or so she describes. Then it died, & will not start. Right now i'm clueless on where to go next.

Turns over = but won't start

Codes: P0120 Throttle/Pedal Position Sensor/ Switch A Circuit

Just recently iv'e replaced
Oil
Oil Filter
Fuel Filter
02 Sensor (front one)
Gas Treatment

It drove flawlessly for 500ish miles after that... now this.
Any help is appreciated!!

Replaced the Distributor Cap

Getting Spark in 2-3 but not 1-4
Distributor maybe?

Howdy, I have same hardone..lol
Throttle pos sensor. Located inder air filter assy.
X kinda looking flat sensor with top connector.

Multimeter it if memory serves its .35 or 3.5 to .45 or 4.5
Also there is an adjustment screw, not a lot of adjustment, so if out of range, change it. Middle of the road is 30 ish, bosch 60 and up. Hope this helps.
Fyi...it is the one on right side facing from front of truck