the truck has about 8000 hours on it. I am using a handheld CO detector. Plugs, cap, and rotor are all in good shape. I did a little research and was able to adjust the air/fuel mixture. There is a little screw under a cap on the propane converter which i adjusted until the level was back down to.1% or lower. There were no codes. I was just doing the scheduled check and was very surprised when i saw the high numbers. Checked here and the toyota service manual, and decided to mess around until I got it back to normal. Thanks for all the input, hope I could or can help you too.