I have a 2000 accord 3.0L when driving at about 3500 rpms heavy accel the vechicle loses power rpm revs up to rev limiter and vehicle misfires only code is p1399 and the vehicle has new plugs and wires,coils if driven lightly no problem it only happens when trying to pass or heavy on throttle i'm thinking cat converter but wanted to see what others think or have seen

 

Welcome in,that is a good guess,the only way to check is take it off and run a test pipe,how ever it may be a bad TPS,the throttle position sensor is a potentiometer, and is connected to the throttle valve shaft, as the pedal is depressed the voltage is increased and the signal sent to the ECM/ECU for computation.

 

the cat converter was broken and clogged but after replacing and test driven it still has a problem at 3500rpm no codes seems like vehicle is running rich though fuel trim on my cheap scanner only shows bank 1 and short and long term trims looked ok.Not sure about TPS never had 1 cause a misfire.I'm not sure if disconnecting battery resets adaptives or not but I did that and after learning all monitors the car still did act up again but to me not as much as before and i was able to pass vehicles at 80 mph. Any ideas would be greatly appreciated