Will a leak in my muffler cause rpms to increase slightly ?

This happens in neutral as well as when in gear.  Only talking 2-300 rpms in each case.  Will be replacing muffler tomorrow regardless.

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I think I have a similar issue, for the same reasons. I'll be very interested if you could say if it works please ?

BOB J (author)  steveastrouk8 years ago
I felt exactly the same as Burf but not the case.  Replaced muffler but rpms still running high.  Had a code check done as Check Engine light came on.  Results were: #4 cylinder misfiring with several possibilities listed.  have not corrected as yet.
steaveastrouk, FYI !; don't know if you are aware, I was not:  Auto Zone will do a free error code check for you & give you a printout re same. 
i'm with burf on this one
If there is a hole in your muffler, there may be holes or even a barely noticeable cracks elsewhere in the exhaust system too. Your vehicle might have two oxygen sensors; one before the catalytic converter, and one after it. Any leaks  around the
converter or 02 sensors would probably make a noticeable difference.
.  Sounds like a reasonable/probable explanation, but I'm guessing a leak that large would trip an alarm and light something up on the dash (eg, Check Engine). Maybe not.
.  While the car is up on the rack, I'd ask the muffler tech to double-check everything from the cat forward.
Re-design8 years ago
It might if the leak is large enough.  If it was the it might be changing the O2 level and the oxygen sensor might be picking that up and sending a different mix to the intake.

Or not.  But 2-300 rpm increase is not insignificant.  It should be enough to cause the car to creep at stoplights when it didn't before.

Don't forget to come back here tomorrow and let us know what happens.
Burf8 years ago
It could, by reducing the exhaust back pressure. When exhaust back pressure is reduced, less work is required to expel the burnt gases after ignition. Less burnt gas in the cylinder means that more fuel/air mixture can be injected into the cylinder and more fuel means more power and better combustion.
One caveat though, most modern engines have a tuned exhaust system that relies on a defined amount of back pressure to prevent the fuel/air mix from just shooting through the cylinder and out the exhaust before the exhaust valve can close.