2.3L ('83-'97) 1989 2.3 starts then falls on its face

[OldMan89]

My old 89, 2.3 5 speed, starts fine every time. But right after it starts and rises to its initial rpm it falls to just over 500 and the check engine light comes on. After a few minutes of warming up it will either rise to 1100 and fall a few trines or it rises to 900 to 1000 and the check engine light goes off. Runs fine down the road. And once it’s warm it has no issues. At first I thought bad gas because I’d let it set for a while with 1/4 tank. Filled it up and it didn’t do it again for several days of driving. It then it started again and it seems to get worse as time goes in. Any insight would be great.

 

[MT_PLS]

Have you pulled any of the codes to see what is setting of the CEL? That would be a good place to start.
Go here to get the codes.