Just a heads up if you have same problem with no codes. I had a very low rpm stumble... Started from out of the blue, did plugs/wires, opti died anyway replaced it too, coil, ICM, used old cpu, checked all connectors and so on no fix.... Turned out the MAF was carzy and no codes, used MAF 35 bucks all fixed... Waisted lots of time but most of it needed done anyway... NEVER LET YOUR CAR SIT FOR 1 YEAR IT WILL HATE YOU!!!!

Ohhh and it got worse as it got hot!!!

 

Congrats on finding the problem. I let my car sit for about 2 years, bad idea. It took me months to get it running good again due to problems like you had that were hard to track down.