exhaust running rich.Please help!!!

hello my 94 grand am's ehaust is running rich. Here is how the problem started. When my car would sit there in park an idle it would keeping reviing up like I was getting ready to race. It eventually quit doing this and the exhaust started smelling. The back of my car is black from hte smoke. Some one told me this is my O2 sensor. Could they be right? I tried to use a diagnostic key but it does not work. The people at Autozone said that it is probably a fuse or the box you plug the key in is bad. Any ideas would be greatly appreciated. Thank you

welcome to the forum. I would agree with the 02 sensor. It could also be a bad MAF, or a bad IAT sensor. - these could both potentially cause it to run rich. Do you have any check engine lights / service vehicle lights?

yes, the check engine light stays on

Then your best bet is to take it to a place like Autozone or Advance Auto - they'll be able to read your codes and tell you what's wrong - for free.

94 and up grand am's need to be read with a scanner, you can't do the trick with the paperclip on them. You can do some serious damage to the ecm and other components by shorting 2 terminals. I agree, get them read at autozone for free, nothing wrong with that.

okay, so now here's what has happened. I have found out that the previous owner relpaced the motor. Instead of what originally came in it there is a 3300 motor. I went and bought an o2 sensor and replaced it. I also replaced the spark plugs and now the car is hard to start. Once I do get it started black smoke rollls out of the exhaust. Do you think I got the wrong o2 sensor and should put the old one back on?

Its possible you got the wrong o2 sensor, black smoke when you start the car indicates its running rich. Beware, you can wreck the cat if you are pumping too much gas, and it gets into your oil as well.

It already ran rich before. Black smoke used to come out but now that I switched O2 sensors pitch black smoke comes out. Do you get what I am saying? I think I am going to have my father put the original O2 sensor back on and send it to the hospital monday.

Put the old o2 sensor in, and check your air filter and the duct work leading from the filter box to the throttle body. Something might be clogged, and an extremely dirty air filter will cause it to run rich, also the maf sensor, throttle position sensor, and your idle air control valve. Is the inside of the throttle body clean?

I will check the throttle body and get back to you

What motor did you get the plugs for??

The stock one, or the one swapped in?

the one swapped in

Simple check....give the plugs a look over quick. Make sure you didn't accidentally knock an electrode in or foul a plug.
Does it very when the car is warm or cold?

The car will barely run now

Plug wires out of order??

so you are saying that if the plug wires are out of order that could cause the car to go from running a rich light black exhaust fume to a pitch black exhaust fume?

okay so now I have replaced the spark plugs and the wires and it runs better. The exhaust is not as rich but I still have not figured out the problem. I was thinking that maybe I should try the new o2 sensor again. Any ideas?