I have an 05 GT with a Paxton 2200 and Pypes H-pipe. Car has 56k miles and has always run great! Recently I switched my flowmaster American thunder's for Magnaflow axle back mufflers. I bought the Magnaflow's used, they are a little beat up and I know they are leaking. Since I switched mufflers the car has a miss at idle, still idles and drives fine though, can an exhaust leak cause this miss? I don't have a CEL. Thanks

 

I can't imagine that changing axle backs or anything beyond the rear O2's could have an impact on engine idle since I doubt that the differences in backpressure are that significant. If a good TB cleaning and tank or 2 of SeaFoam doesn't clear it up, I'd swap back to the Flowmasters before replacing other components to see if, in fact, it IS the mufflers. Then go from there.

 

clean maf sensor as well

 

I cleaned MAF and TB, drove the car for a few days with no changes. It also randomly started hesitating in 2nd & 3rd gear when coming into boost (3k rpm range). Switched back to the flowmasters and the car is running great. I can't believe Axle Back mufflers would make such a difference!? I loved the Magnaflow sound and maybe it was just these mufflers were crappy and/or plugged up, who knows. On the hunt now for a quieter axle back...