When engine has warmed up it misses and loses power

That is correct. We can't do without the exhaust system. It could be a restricted exhaust but this normally doesn't happen when the car is warm. Plus you can confirm this by pulling the o2 sensors and see if it runs better as this gives a place to bypass the clog.

Here is a guide that covers loss of power issues. We need to go through this and see what has not been done and then check that. I would suspect this is more of a sensor issue like the air flow sensor. Basically when the engine warms up the PCM starts running the engine based on the sensor inputs vs the PCM's preprogrammed parameters.

Let's review this guide and then go from there. Let me know what you find. Thanks

https://www.2carpros.com/articles/symptoms-of-low-engine-power

Hi,

A plugged catalytic converter will cause a power loss. However, if they are plugged, you should have diagnostic trouble codes stores. For example, P0420, which indicated an issue with the converter. Also, keep in mind fuel pressure can also be dropping and causing the power loss along with other things.

Since you have taken it to a shop, was the computer scanned? If so, were codes found and what were they?

If you want, take a look through these two links. One describes common symptoms of a plugged converter and the other how to test one.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Now, the link indicates to remove the converter. Try just removing an O2 sensor before the converter. Although it will not be perfect, if the converter is plugged, you should notice a difference with the sensor out.

Try that and let me know what you find. By the way, you can't use o2 sensors if it has a straight pipe, so they are being honest. Also, the vehicle's emissions system is required based on federal law, so by law it can't be modified or removed.

Let me know.

Joe