Car is running fine except, when in a hurry and press pedal down to get quick power to over 3 RPM's to get to next gear (mine is a 5speed ex sedan)
then car goes CHUGG CHUGG CHUGG and then takes off as normal. It does this on each gear shift up to 5th gear and then also runs fine.
But that lack of power and chugg chugg chugg comes only when in a hurry and trump down the pedal to quickly get moving and rev up to 3 RPM or more.
I changed fuel filter, spark plug wires, air filter. But cant figure this out and not sure if even dealer service dept will take the time to properly diagnose
since 1990 and takes time on the reader to check codes. Had to 2 mechanics already and they are stumped. Said i need to have codes read since they
tried the normal things that might be wrong. If I drive normal around town and not in a hurry and not needing that extra power, then the car is smooth running and great.

A Mechanic already checked catalytic converter (original to the car) and he did find the inside Honeycomb all broken apart.
mechanic then removed the inside broken pieces and attached catalytic converter back on car.
He test drove car and it still had same symptoms. So he assumed it was not caused from the catalytic converter because it now is basically an empty pipe attached to the rest of the muffler piping under car.
So he is not understanding what it is at this point.
All help is appreciated because I am trying to get the car ready to drive 1500 miles in the next week I hope.