I hope to not be too vague as I don't know a lot about cars.

I recently purchased a 1.2L Fiat Punto II 2005. It has trouble with a rough idle, a power drop off around 4krpm when accelerating and a general sluggish feeling to the acceleration. There is a hole in the Flexi part of exhaust also. After driving for a couple days I can tell fuel consumption is much higher than it should be

Returning codes: P0300 - random/multiple cylinder misfire P0170 - Fuel Trim Bank 1 P0130 - O2 Sensor Circuit bank 1 sensor 1

Now from the researching I've done it seems the hole is likely caused by burning fuel after misfire on the exhaust, so I don't want to replace the exhaust for the new one to burn through too.

On the other hand It seems that the hole may be tricking the car to think it needs more fuel to the point it is too rich and can't fire under load?

Any input from more experienced persons would be much appreciated!


1 Answer 1


Fix the exhaust leak, impossible to diag properly with a leak. Then look at O2.

If your car has been running rich for a long while, your catalytic converter is likely bad or going bad.

I would also check for vacuum leaks, that gets the engine running rich (sucks in too much air.) Actually now that I think about it, maybe it'll run lean. Unmetered air and all that. Anyway, good idea to check it.

  • So exhaust fixed first then just try diagnose problems from there, without running car too much incase of further damage? That is my biggest concern, fixing one problem to find another and fix that once it's damaged the first again :/ Thanks for the speedy reply! Commented Jan 8, 2021 at 17:00
  • The theory of operation behind the catalytic converter is that an O2 sensor "upstream" measures oxygen content in the exhaust gas, then a "downstream" measures it after catalytic conversion. If the upstream O2 sensor is bad, the engine will add fuel to compensate for what it thinks is a lean condition. This spew out petrol in the exhaust, and clog up the catalytic converter. So, replacing the O2's often unmasks a problem with the cat.
    – lericson
    Commented Jan 9, 2021 at 13:53

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