under normal driving condition, the car would jerk every so ofter as if it was gonna die.

critical info?
currently running on a p05? cx ecu for the time being
possible vacumm leak, idle jumps 1K-1.5K

obd1 LS

 

A couple of reasons for that. LS is made to run with a 4 wire o2 and running it with a 1 wire 02-ecu(p05) will cause it not to run right. Also, the p05 is starving your LS motor of fuel which will cause your car to jerk every once in a while. And last, you do not have a vacuum leak. The p05 ecu is causing your idle to jump. I recently had to run a p06 ecu on my LS due to a bad chip on my p75 and i also had the same idle problem as you. It was caused by the p06 ecu. As soon as i got my new ecu installed, the idle problem went away with out even touching the engine. Get rid of that ecu and most of your problems will be solved.

 

you cant expect the car to run right with the wrong ecu...

Get the right ECU and then go from there.. you shouldnt even be driving the car like that.