1997 Ford Escort idle problems

I have a 1997 Ford Escort sedan with 88,000 miles on it. The car has had regular maintenance for the most part, but has recently started experiencing problems. About 3 months ago, the Check Engine Light came on. My finances have been very low as of late, and unfortunately, I just let the light stay on. Eventually, it went out, and I never experienced any problems with the car running. It came on a couple of times later, but still no visible signs of problems. Then, about a month ago, my car would start idleing roughly when the engine warmed up. It is like a surging type idle, like it wants to stall, but never does. If I run the air conditioner, it stops, assumingly because the air make the car idle higher. At the time, I thought it might have been bad gas, so I ran some fuel cleaner and a tank of premium octane, to no avail. Now, within the past two days, it idles rough not only when warm, but also when I first start the car and it's cold. All this, mind you, with the check engine light off. I'm pretty sure it's not the battery or alternator. The battery is 1 year old and the headlights work fine even at rough idle, and I get no battery indicator light. Most people I talk to think it is probably something as simple as a tune up. I worry it could be a clogged fuel filter, bad transmission, fuel pump, etc. As you can probably tell, I am not mechanically inclined at all. As I said before, my finances are VERY limited due to personal problems. Is there a surefire way to tell what the problem would be without a battery of tests and procedures? Does it sound like it could be just a tune up problem? That is my hope, because I have a brother in law that is capable of doing that for me. Thank you in advance for anyone's help.

Mike