Cheeky here with a few questions. Never owned a bonneville before, just got this baby with 90k on it from the original owner. I'm having an intermittent service engine light. Car runs decent, my mileage is a little off though. Somewhat of an off idle, its high at times and low at others. I figured o2 sensor, so being only $15 i changed it. Didnt notice any difference and SEL is still on.

So i got an OBD-1 scanner and got a code 13, 21 and 41. How many o2 sensors are there and where are they located? I replaced the upstream i believe, where the manifold connects to the cat. Also, where are the other two sensors (throttle position sensor & camshaft position sensor) located? How should i go about figuring out whether its the sensors or the connectors/wiring besides visually inspecting them? Last but not least, any advice or known issues you would share with me would be great too.

Welcome to the forum!

You should find these to be of interest:
http://www.pontiacbonnevilleclub.com/forum/1987/topic745.html
More specifics for P0021 http://www.obd-codes.com/p0021
More details for P0013 http://www.obd-codes.com/p0013

Location of camshaft sensor is below the left side of the waterpump as shown near bottom of posts here http://www.pontiacbonnevilleclub.com/forum/post383853.html?hilit=cam%20position

Since all of the codes are linked to the cam position sensor, it could be a bad sensor, problem with the wiring, magnet or ECM.

Thank you sir, I forgot I posted on this website and just saw your reply. O2 sensor was an easy fix, Bosch didn't work but the delco worked fine. Changed the cam sensor and that code went away, changed the tps and that code went away also. It was kind of difficult adjusting the tps because I couldn't get the leads on my volt ohm meter inside the tps connector. Ended up getting a sewing needle and sticking it in between the wire and the connector housing and touching the meter leads to the needle. Cars been running like a champ ever since.