My 1997 cadillac sts idles very rough

There are two easy tests for the catalytic converters. One, use a infrared pyrometer and measure the temperature of both catalytic converters and compair the readings. There should not be much difference between the two if both are flowing correctly. Another easy test is to drill a 1/4" hole before each cat and check for excessive back pressure.

bad coil packs

Only got a jumped timing chain or head
gasket left

True of many cars. Happened to me too many times, fourin
or domestic.

run a good injector cleaner through it like STP gas treatment or Gumout injector cleaner. Might have to do more than one treatment - good practice add one bottle about every third or fourth tank fill.

Resolve trouble codes and try again, if car runs ok no problem if not, write again.

Keep an eye on your temperature gauge until we figure this out, just in case & see if it climbs much/any at highway speeds.

service engine

I have a 1994 Cadillac Eldorado and every time i start it the car has rough Idle and the Idle fluctuate's. I also can feel it in the gas pedal when the car is doing this I tried replacing the throttle body sensor but it still does it I also was told it was the Idle error sensor. So instead of spending the unecessary money again I thought I would go online and see if anyone could help me with this problem.