Try what I suggested first. If it doesn't work then reply that it hasn't. There's no reason to go into advanced trouble shooting if you haven't knocked out all the simple potential problems first. Most of the stuff I listed needs to be done for your 90K maintenece anyhow, so it's not a waste to do it even if it doesn't fix your problem.

Once you complete it, disconnect the negative battery terminal and pull the 80 amp fuse out of the fuse box under your hood. After about 15 mins, put the fuse back in, reconnect the negative battery cable, and then turn the car on. Make sure the AC and radio are off and let the car idle for about 10 mins. Do not hit the gas, just let it sit idling for the 10 mins. The ECU is "reprograming" itself during this time. After 10 mins, turn the car off, wait a min, then turn it back on.

If you get a CEL after all the maintenence is done and the ECU is reset, you may have a bigger issue. But this very well may resolve the issue.