Ever since I replace the engine in the bonne it has been idleing roug. It goes from a normal idle to very low (almost to the point that it dies) and it rarely (2-3 times a week) actually does die. I pulled the codes and it says cam sensor. However the car needs a cat, the one on there is drilled out (IL doesn't require emissions til some time after you get your plates) and the oxygen sensor maybe/probly is going and just hasn't set a code. Would a bad O2 sensor cause a rough idle or should I replace the cam sensor? Also could the cat being drilled out be causing this? I'm ordering a hi flow cat on my next paycheck and a friend of mine is gonna weld it on for me and weather the o2 sensor can cause this or not I intend to replace it then, but is it likely that its something else?

Please use the Techinfo procedure to pull the codes from your car and report them back. We'll need a little more information to go on, this could be as small as a vacuum leak or a much larger issue.

Also more information on the engine swapped in would be good. Was it a JY motor or a rebuild. My reasoning for asking is that on a JY motor swap typically sensors etc are used and a different year motor would possibly have different sensors.

The only code it gave was 41 which is a cam sensor. It was a JY motor and I don't believe it came from a bonneville because I had to switch to oil filter adapter because the one it had didn't have output for an oil cooler, and there was one sensor on there that needed a differnt wire connector than what was supposed to connect there so I switched it out with the one from the old engine.

Cam sensor could cause issues. You need to know what that motor came from to properly diagnose the issue.

Could be a different year that the sensor/positioning on the cam gear is different..or it might be just a bad cam sensor/magnet

either way wouldn't the solution be to replace the sensor/magnet?

also I thought if the cam sensor wasn't working right it would occasionally keep the car from starting? because the car always starts right up

Verify the magnet is in place when you pull it apart.

Keep in mind that the code 41 may be an ICM (ignition control module beneath the coils), crank sensor, or cam sensor. The Cam sensor signal travels throug the ICM and crank sensor before getting to the PCM.

Inspect your connections at the ICM and the crank sensor harness to make sure nothing is damaged.

Do you have an ohmmeter? If so, check the wires:

Brown/white wire from the cam sensor Pin A to pin J at the ICM. Should be very low resistance (continuity).

Check the ICM Pin M (red/black) to pin B on the cam sensor. Should also be good.

Check Pin C of the Cam sensor (wht/blk) to pin M of the ICM.

Do you have a spare ICM from the old motor to swap in for troubleshooting? Do you have any bent pins on the ICM or it'* connector? Any corrosion?

I'm in the process of moving so hopefully I'll be able to dig up my multimeter. Unfortunately I sold the ICM from the old engine. Actually the break lines on the bottom of the car were rusted out and I hate repairing break lines so I gave it to a mechanic in exchange for him fixxing them. Anyway isn't there a way to test the ICM? Also no bent pins or corrosion that I can see.

ICM testers at auto parts stores are a joke. They test bare minimum generic functions.