I have a '92 LE V-6 with only 113,000 miles on it. MPG has decreased from 20 mpg to 14-15 and now have these codes. Should I replace the speed sensor, thermostat and temp sensor as well as the O2 sensor because none have been replaced and are all easy to do so, or is there something else that I should look at as well? I love the power on this old baby!

 

If those are original it would not hurt to replace with good new ones. You may have a plenum gasket leak. There is a lot of info on this site. Look for oil inside the intake manifold. If it is the plenum gasket you will start to get other performance issues.

 

Everything is clean of oil from injector to plugs. Had professional injector cleaning done two years ago just trying to make sure things were good. She is not sluggish for sure, as I said mpg is a little low and the reason I checked the codes was at times shifting to overdrive is slow. I do have one of those switches to cut OD off but it is not lit. I don't think the plenum gasket is a problem, for now. Any other suggestions?