May be cat or o2 sensor not getting hot enough
Thanks for the welcome.Welcome back.
You removed the exhaust manifold and found there was no catalyst and no reason for it to be missing. Did you check to see if maybe it deteriorated, broke up and ended up downstream in the rear converter?
Welcome back then
Do you have access to a scan tool that can read live data? Would be interesting to see what the short/long term fuel trims were at idle and when the problem was occurring. Strange that the engine rpms are going up but the power is going down. Doesn't seem to compute.
I'm planning to stay on the cheaper side, definitely not looking for the best. I'm not a mechanic and not a tuner. I don't work on other people's cars. But I will assist a neighbor or somebody stranded on the side of the road occasionally.I have a rather expensive Autel, but I probably wouldn't recommend it to anyone. Some of the touchscreen icons don't work and Customer Service leaves much to be desired. I have heard some good reviews for Thinkcar scanners. Some Pros that I follow are happey with them and they have models that cover a wide range of functions and prices.
If you are planning on dropping a few hundred, do some serious research. Check to see how updates are accomplished and how much they cost. I think all the tools will work without constant updates, but if you work on more than one vehicle you might find them necessary. Last year I paid $365 for a one year update plan. Am now skipping at least one year.
If you can work with the cost, a scan tool with bi-directional controls is very handy. I use those all the time.
Amazon has a huge selection of scan tools that you can investigate to find out particulars and tool brand websites are a good source for specifics.
Good luck. Beware those that say "Brand X" is the best. There is no such thing as the best, unless you are prepared to spend thousands for the particular Manufacturer's dedicated tool. With that you are locked to one brand of vehicle.