My Mazda MPV randomly begins to "chug" and act like it will die at a stop. the check engine light comes on. Started about 6 months ago. Seems to happen more when it rains. If I tighten the gas cap it stops and 1/4 tank later the light goes off. It does not happen exclusively after filling the tank (ie- filled it last week and it began doing this at 1/4 tank left- though the cap has not been touched since I filled it.)

when the battery died it probably activated the immobiliser system. Try using a scanner to reset the immobiliser.

Might be the Brake Booster do you have a CEL coming on?

do mobile power onpassword {4-8}

have u checked ur spark plug leads and spark plugs it all so be ur injectors

Hi you need to have a diagnosis on why the engine light was on in the first place. By disconnecting the power source to the onboard computers on connection they have probably come up with a mismatch due to something being outside it's set tolerance. The reason it stops when clutch is depressed is you are removing the load from the engine. A fault code reader needs to be plugged into your vehicle, hopefully the codes will still be there as sometimes they might be removed when power is disconnected. Good luck

Did you check the transmission oil?

have you checked your fuel pump and relays for fuel system? AND , have you had the obd codes run yet? That sounds like the places to start_fuel system/delivery. Oxygen sensorswould be my next shot. maybe one wasnt replaced or came loose during new cat install. have them double chk that for you.

Sounds like you are having random misfires of your plugs which could indicate a need for a tuneup (or if you've changed your plugs, you didn't use the OEM plugs). What's your mileage? Is your check engine light coming on?

see a professional

Drop in to autozone, or Pep boys and have it scanned, free, for trouble codes then go from there. Could be something simple & cheap