99 4.6L rough idle, acceleration
 

I have a 99 F-150 with a 4.6L & about 120K miles. When I would sit at a light it would sputter a little now & then, & if i stepped on it sometimes it would misfire. I tried some Sea Foam which seemed to work for a bit but one morning it began running rough while accelerating & the service engine light came on. I cannot check the codes, because for some reason the reader is not wired. I have changed the plugs, wires, coil packs, EGR valve, sensor & hoses. It now idles smooth until putting it in gear. It runs rough in gear or when I rev the engine. Any ideas?

check the fuel filter

Changed the fuel filter, no change. Idles ok but sputters when you rev it at first, then fine. Put it in gear & it begins to idle rough. Could it be an injector?

Yea, snake-oil is never the answer.

If you can't scan it, that should be a priority fix. Take it in, they'll clean the terminals for yuh and check feed/communication. Could have a PCM problem, it happens and why it may be acting up.

Other than that, the first thing to check is fuel...fuel is always first, it's a good by law and saves time and money.. With that, check fuel pressure. If weak, change fuel filter and re-check. If pressure is below 32 psi, time for a new pump. It was common for the original the pumps in these models to begin to go south anytime after 90,000 miles.