Replaced the MAT sensor on Saturday, since the Diacom indicated it was reading -13* (that's minus 13) in open loop (uhh... a slight problem!) after replacing, it seems to run even worse than before! I Checked that all vacuum hoses and sensors were hooked back up correctly, but the car now acts like it's running on 6 cylinders. RPM is fluctuating up and down ~1k at idle, lacking power, and still seems to be running rich. Basically running like a POS. I am going to replace out the plugs, cap, and rotor this weekend, as well as double check the timing... anyone else have a similar experience or have any idea on what to check next? I'm wondering if maybe something isn't quite right with my ECM, it did seem to run a little better when I borrowed one that I know is good, but still ran less than perfect. Maybe I'll grab one next time I'm at the boneyard.

 

I would be more suspicious of a vacuum leak after you R/R'ed the intake plenum and runners. Check your scanner again and see if the new sensor is reading "sane". If it is, you fixed that problem but caused another during the install procedure.