Chrysler Repair: 2004 Stratus 2.4 backfire, exhaust leaks, 2004 dodge stratus

Question
Hi

Lately I have some problems with my 2004 Dodge Stratus 2.4 DOHC.

It Backfires into intake mainfold.
Especially on acceleration, when car is on Park, also pushing accelerator pedal rapidly it  making laud backfire.
It happens on cold and hot engine.

What should I check before to start replacing good parts?

What I know about vehicle:
No stored codes
TPS in correct (cheked and confirmed)
O2 sensor is moving very slow (checked and confirmed with pro)
exhaust is leaking in middle and at the end after O2 sensor.

Lately I've changes spark plugs to Autolite Platinum.
Fuel economy 8.0 highway to mixed 11,0.

Thanks in advance
Chris

Answer
Hi Chris,
Absent fault codes I would start by correcting the exhaust leaks as that can cause O2 reading errors which then causes incorrect injector pulse width and loss of fuel economy. and also may be the source of the backfire gas.
Then keep checking for fault codes.
If the upstream sensor doesn't set a code but does show slow movement you might help this out by replacing the sensor. I would be reluctant to change anything beyond that until making those corrections.
Please see the PS below and respond.
Thanks,
Roland