Hope that someone can help! This s-10 blazer is my baby, I have had her 8 years and she has never left me on the side of the road... almost three years ago her fuel pump
went out as I was leaving my driveway. needless to say my husband is not a mechanic, so she sat..... she was running bad before that. well I put her back together. cleaned the gas lines, new plugs & wires, new coil, new rotor, checked for vacume leaks, you name it I have done it. she did not pass emissions. she did great at high rev but fell on her face at idle. she lopes at idle, I know that theres several sensers but which one? I dont have a lot of money to be buying them all but some where to start would be great.......
if any one has any ideas i would really be grateful. by the way other than this problem shes running better than she has in a long time..

 

It doesn't sound to me like a problem with a sensor at all. I don't which engine you have, so I'll try to be general. Anything that will cause it to idle rough will cause it to fail the emissions test. You should look for vacuum leaks, particularly where the vacuum hoses connect to the throttle body. Start the engine and let it idle. With the engine running, spray some carb and choke cleaner (Gumout, etc.) around the throttle body and vac. hoses and see if the idle quality changes. Don't over do it, just a little squirt on each line will be enough.
If that doesn't show anything, you should check your EGR valve for a leak. Remove the EGR valve (make sure the engine is cool) and turn it upside down. Carefully pour some liquid (water will do) in the part with the valve in it and let it sit for a few minutes. It should hold the liquid without leaking. If it leaks, then you need to clean or replace the EGR valve. Either one of these things will cause both a rough idle and failure of emissions test. HTH.
Good Luck and God Bless,
Revredneck

 

pull a plug or two and see what they look like.