Ford Repair: 94 F150 check engine light, air control valve, oxygen sensors

Question
1994 FORD F150
PICKUP
5.0L V8 FI OHV / REAR WHEEL DRIVE
3 Speed Auto (with Overdrive)

Check engine light came on...took to local shop next day with following results:
Coded 212 in memory for 'loss of PIP signal'...tech said spark plugs are a little worn and they found a chaffed area on a plug wire and taped it up...also said distributor cap is somewhat 'burnt'(cap and rotor were replaced in 2005)... I drove it the short distance home from shop and 'check engine' light reappeared...so I replaced the dist cap and rotor...drove for about 20 minutes and runs great, then 'check engine light' came on again...after about 15 more minutes it went off..came on again and went off...plugs and wires are 3yrs/25k miles old...no noticeable difference in performance when light comes on.  Thnks, Rich

Answer
A light that comes on and off usually points to either a oxygen sensor or idle air control valve. If you don't have a strange idle you can probably rule it out. Change both oxygen sensors and you should be fine. The money saved in fuel economy will out way the cost.