86 Mustang needs some help

[FoxBody]

3.8L V6 automatic trans
Runs rough and sputters on accelration sometimes while crusing. At first thought it was bad gas but this problem has persisted thru a couple of tanks. Sometimes it runs and idles great but when least expected it goes bad.
1. how do I get trouble codes on this year, I think this would help. I have the manuel but I think it explains a different or newer year model

When crusing at highway speeds it sould like the engine is clattering, when I give in gas it stops, During hard accelrations no knock except at top end before shift there is a dat-dat-dat-dat knocking but goes away during accelration in the next gear.

If this helps there was a lifter clicking during cold starts, replaced the lifters ..... lol it still clicks on cold starts. This stang has come a long way since purchase, when I got it home I found that the wiper fluid hose was connected to the manifold vaccume, it sucked instead of spray..... lol

Thanks for any ideas in advance.