Troubleshooting

[Durandal]

I just got a 1993 J-Spec supra tt and although I've been reading forums for quite awhile on possible problems before I even got it, some things I am unclear on.

When I turn the ignition on all my dash lights come on except for the cluster on the right with oil level, oil temp, and check engine and nothing in the little screen above those although that one kind of looks like nothing would display there anyway.

The reason I'm asking is I have been getting a warning light come on randomly when I'm driving and sometimes it goes off but mostly stays on. At first I thought it was a problem with the active front spoiler's auto feature which I found people with aftermarket stereos have problems with. I do have an aftermarket japanese stereo that was in the car when I bought it.

Some times when I start up the car, mostly a cold start, I can hear kind of a rattling coming from the back end and it idles low around 500rpm.

So I'm starting to get paranoid and want to do some troubleshooting. When I jumper E1 and TE1 in the diagnostic port 1 or 2 nothing happens to tell me if there are any problem codes.

Does any of this sound familiar or does anyone have any trouble shooting tips I can start with?

Thanks and sorry for the long post.