Quote Originally Posted by Spartanzz View Post
So i have had my Grand prix GTP for a few weeks now and we have been trying to find out what should be replaced to make the two codes i have go away. The codes came on after i went WOT and then let off and the codes are P0303 Cylinder 3 misfire and P0171 system too lean. I have been told many things like i should replace my plug wires and plugs, i should search for a vaccume leak somewhere, and also that i have a lazy upstream oxygen sensor. so i am wondering if any of you all have had this problem and could help me find out what i have to replace to make the codes go away so i can get an emissions test done soon. Thanks
With any misfire, check spark plugs, wires and coils. If you have P0171, you probably have a big vacuum leak. Do you have access to a scanner? If so, scan your IAC values at idle (after car is warm). They should be between 45 and 55. 01gpgt01 gave me this tip, and I found my vacuum leak an fixed my P0171 code. Also, scan your O2 values. That will indicate if there is a problem there.