Changing a muffler should have no effect on idle and should not require retuning. Just based on information from this and other forums, no one who has swapped out a muffler has reported anything like this, at least to my knowledge. Mustang Enthusiast magazine did a header, true dual (H) installation and muffler change on a V6 and reported no such problem, although I don't think they changed the stock tune.

The only thing you can easily do is reload the stock tune and see if that fixes the problem. If that doesn't do it, I'd suggest you take it to your dealership and have them take a look. It is quite possible that you are having a problem not related to the exhaust system. Also, from what you said, it sounds like you got a custom tune from your tuner, you might want to let them have a look before you go by the dealership, although, again, I can't imagine a tune that would be that sensitive to adding duals, but stranger things have happened.

 

this is a long shot!
Check your Cold Air Intake and check to see if everything is nice and tight .

Just trying to help

 

Denny:

I actually havent added an intake yet because I was waiting on getting the Supercharger.

However I was retracing my steps for that day.

After leaving the shop who put the duals on I got gas at a new place. It said 93 Octane but it was a little shady hole in the wall.

I have always gotten my 93 from Exon by my house.

What are the effects of a 93 tuned car that uses a different octane of gas? Would it run pretty sh!tty?

Everyone who has listened to it putter around back by the exhaust swears it is a fuel issue

I am going to run the tank out tomorrow then gas up at my usual place. Maybe I will get lucky

 

Your horse is looking really nice!
Maybe you got a (bad hit) of gas. When you run that tank of gas down, you may want to put some Lucas, Redline or Royal purple gas or engine treatment in the tank. Do the research before doing that. I'm not sure of which one you need to clean the gas line out.

Just trying to help.

 

I appreciate the help Denny and thats a good idea

Hopefully the new gas will help and if not I will head back to the shop that tuned it

It is weird, it only has problems while idling. Havent had any issues taking off or anything

 

Have you tried just simply re-loading your tune? I had a strange idle problem once... I simply reflashed the car and it fixed it... and it's never come back...

 

Scrming: I will have to go back to the shop and have it done. I was gonna buy the SCT2 to do it my self but to be totally honest with you I was afraid I would mess something up, so I just had them do it. After reading up on it and talking with folks on here it seems very easy to operate.

The good thing is that the guys who did it charged me like $375.00 but it would of been $475.00 and I could of took the SCT home with me afterwards.

I am gonna ask them if I can still give them the $100 and keep the thing, it hasnt been that long since the tune. They are pretty cool. Worse case scenario I remember them saying that if I have to come back to get the car reflashed(intake add,tuned back to the factory settings, etc) they would only charge me $75. I should of just bought the damn thing

 

The X-Cal2 is very very easy to use....

Do you know exactly what they used to flash your car? Was it an X-Cal2?

 

This is the one they used, this is actually their website

http://www.modulardepot.com/product_...roducts_id=219

 

ummmm... well... i'm a little concerned here... When you flash a car with an SCT X-Cal2 that X-Cal2 becomes "married" to the car... the X-Cal2 cannot be used to flash any other car until the orginal car is put back to "stock"... so in theory the X-Cal2 should only work on your car until they put your car back to "stock"... hmmmmm.... something just doesn't seem right... I wonder if they have SCT's blessing on what they are doing...