I searched through previous posts and was unable to find any help for my problem so maybe one of you can help me.

I have a 1990 civic dx. When i start the car I have no problems and the engine idles fine. Once it has warmed up tho I start having problems. The idle is erratic and it keeps going up and down and up and down. After a little bit of this, the check engine light comes on, I would assume that is because the engine is idling to low and it sounds like it just wants to die.

My first thought was to pull the code for the check engine light. I talked to a couple different people and they all told me different ways of how to check it, but none of those would work (one way was by finding a wire with a yellow connect on the end of it without anything plugged into it and jump it with a spark plug. he said it should be on one of the strut towers under the hood, but i couldnt find anything like that).

Also, even if I was able to pull the code, would I have to have the engine running and would the check engine light need to be on, or are the codes stored in the ecu so i could still find out even in the car is off.