mx6 exhaust mod causing engine running problems

:confused: my mazda has exhaust mods done and wont run right .it has had the catilac converter removed and a 19 inch long resinator fitted. also have replaced rear muffler with a turbo free flow muffler it is running 2.25inch pipe all the way.the problem is setting idle mixture scew,i do what service manual tells me but cant get idle to stabilise at 650rpm it is also upsetting cold starting also the fumes smell rich in fuel.do you need to diconnect oxygen sensor or do i need to increase back pressure more can any one help please.also my engine is a 2.5v6 with OBII onboard computer

good mods wrong set up...you need more air coming in, thats why smells rich you are not getting a smooth spray coming out of your injectors,your cat back...sometimes bigger is not better..just the right set up is needed.

Shouldn't have any problem with that size of piping, I'm running 2.5" and no problem at all. Check your TPS and idle screws