Engine lacks mid range power when hot
 

When the engine is hot 183f and especially if the A/C is being used, the engine will lose power and snap from about 3 to 6000 rpm. As the problem progresses it will start pinging bad loosing more power, wont idle and will just quite. I was watching the timing on the obd2 and it seemed to run in the 7 to 25 deg range. If you stop the car and let it cool down it will run great again for a few minuites. I checked the rad fans are working and the rad/ condensor are clean. I thought maybe the thermostat was possibly sticky so I replaced it. Mazda thought it was the shuttle valve? and replaced it, it was not the problem. Runs great before it gets hot

What year and how many miles on the car?
Do you receive a CEL during this time?
If so, what is/are the code(s)?
Did the dealer perform a compression test?
How long as it been since the ignition components have been replaced (plugs, wires, coils)?
Did you/the dealer verify the cat wasn't clogged?
Has the engine been clean/Sea Foamed by you or the dealer?
Can't rule out vacuum leak either.

The SSV (Secondary Shutter Valve) was a good move to check by the dealer, though they could have simply tested the valve instead of replacing it (hopefully you didn't have to pay for it).

Its a 2004, never has any engine codes, no compression test but had the vaccum test and was good, I dont believe ignition has been serviced, cat not checked and no sea foam. Thanks

i just had that issue a week ago. I was driving on the highway (hot day) and all of a sudden my car was losing power. When I came to stops the car felt like it wanted to turn off. I just changed my spark plugs, ignition coils, spark plug wires, cleaned the MAF, and cleaned the air filter about 2 months ago. I have a 2004 GT and just under 80k miles on it. does anyone know what else I should replace? Car possibly?

^................both of you check the CAT then!

Actually the first poster probably needs to look at the ignition system as well.....if an 04 and not sure if ever looked at. Probably has a lot of miles on the coils.............and................if truly bad.....we know where this might lead.

We do need more info on both cars and I see Jon316G is in here at the moment, so let's see what he throws up. Compression check might be in order for both as well.

Thats a good start!

Blue pill or red pill time.

Blue pill = sell it and let the next poor bugger worry about it, wake up in your bed and go about your day.

Red pill = Do the compression test, clean the maf, coils, spider gear, giggle rod ..... and just see how deep the rabbit hole goes ......

Sometimes I say to myself why didn't I just take the blue pill, why didn't I just take the blue pill.

cat test
 

Is there an upstream o2 sensor on the cat? I made a pressure test fitting from an old o2 sensor that worked good for me if there is a upstream one or do you suggest a visual look. Thanks for your advise!!!!

There are two O2 sensors on the RX8
The front O2 sensor is a quality wide band O2 sensor located ahead of the catalytic.
The Rear O2 sensor is located in the OEM Catalytic. It's only function is to measure the efficiency of the Catalytic, it does not impact engine management.

^^^
PS: Ya sorry .. I recommend a visual look. It's probably easier to remove the midpipe than the Front O2 Sensor anyway. It's in a tough to reach position and I'm told there is a special wrench available to help remove it.

There are two 02 sensors: front and rear.

If your cat is bad you should get a CEL. However, sometimes CEL does not appear so here are four simple ways to check the cat.
1) Open the cat and see how it looks. If everything looks melted in there your cat is bad
2) Drive the car hard for a while and then see if the cat glows red
3) Let the car iddle and check for rattling noise coming from the exhaust
4) Smell the exhaust (not for too long:))) If the cat is bad a weird smell should come out