What's the code? Take it to Autozone and get the code number (not just the employee's "determination" of the code) and post it here.
If I had to guess off the top of my head, check the connections to anything you may have disconnected during install. I accidentally forgot to plug my MAF back in after I installed my filter, and ran into a CEL and stalling after about 5 minutes of driving. Plugged in the MAF, cleared the ECU, and all was better.
