rough/shakey idle at a stoplight.

I have a 1988 Buick PA Electra. Car idles rough and shaky at a stop light. When warmed up service engine light comes on for a few seconds then goes off. I've changed ignition coil box, wires, plugs, ignition module, fuel injectors, fuel filter. It seems like there may be a vacuum leak. Please help. Car has only 114,000 miles on it and I don't want to give up on her. Before this she was running smooth. Thank you

Well, can check for a vac leak with carb cleaner, spray around the engine, vac lines and joints, to see if there is a change in idle...

If the CE light comes on, this means a code is set.....can jump A to B in the ALDL connector, key on, engine off, and read flash codes....

http://wbo2.com.au/~techedge.com.au/vehicle/im/con12pin.gif

Take the palm of your hand and tap the MAF sensor to see if there is a change in idle or stumble.....

Check fuel pressure? Last time the fuel filter was replaced?

Will check for vacuum leaks. Now the car started making a loud clattering noise. Like metal clattering noise. I had to drive two footed to keep it running as I pulled into my parking spot, the car stalled. No check engine light came on that time. Since then I haven't even started it. I figure it could be a sensor. Also my AC/Heater display keeps blinking randomly on every setting. Something electrical?

Please advise me on the location of E C M on my 1988 park avenue. I have one on the way and would like any expertise on where it is and any other issues to do with installation. Thank you.

New update on 1988 buick PA 3.3. I had someone come and drive my car around the block. At corner near my house there started a metally clattering noise. People were saying its internal motor problem, blown head gasket, rod knocking. Which I just had to laugh. I have excellent compression, car never overheated. Noise was coming from pulley area. Noticed bottom pulley harmonic balancer peice in middle was worn causing the metal clatter noise.
I haven't installed ECM. I;m going to change balancer first.

Also one more question: Is the O2 sensor supposed to feel all loose? Like you can wiggle it back and forth? Please let me know.

thank you again for the previous replies.