My 1994 Saturn SL died completely when driving on the interstate due to a clogged catalytic converter (after many hours of diagnosing everything else). I have replaced fuel pump pressure regulator injector and filter. Car will start but idles rough below 500rpms and dies shortly after, if I can keep it running it stumbles when it hits 1500rpm. I have checked spark and fuel pressure(which after replacing everything but the lines it should and is perfect). I am hearing a vacuum leak (replaced the main known issues intake and throttle body (tbi) gaskets). Still hear it and cannot find it. I am wondering if I have misplaced vacuum lines or am overlooking something. I did do the home smoke test which is blow cigar smoke into vacuum lines and see if smoke comes out. It came out of the butterfly valve. I took off the throttle body again and noticed the iac is completely retracted. Is this normal for cold starts?
I have seen where the ignition coil pack can short out internally sometimes which can cause the problem you are describing. Unfortunately testing it is difficult. But if the part is old and has many miles it should be replaced anyway. Also bad plug wires can do the same.
Yon can try this testing procedure to check the quality of the spark being produced.