after i got my new engine done it seems to have the dreaded surging idle. i cleaned all the connections even got the frrp idle air adjuster. seemed it would just do it whenever it wanted. even worse with the acessories on. it almost wanted to stall. my mufflers seemed to be about 8-10 yrs old according to the receipts from previous owners. they were the standard flowmaster catback setup. sounded tons louder after the new engine. but it didn't sound like a reg mustang. so anyway my question is after i put on the new dynomax mufflers it almost idled perfect. every so often u get a slight hickup so i guess it was missing the back pressure? oh yeah forgot the flowmaster were so bad off all the baffles and such had rotted out and it sounded like a marraca. anyone else have this prob? or knwo why it make such a drastic difference?