[GTMaster]

Exhaust manifold gasket failure doesn't effect the idle (haven't experienced it ever), it just makes the car noisy and the engine bay gets filled with smoke (if it's really bad then some may get into the cabin) but since it's directly under the inlet manifold you can have it replaced as there's more room there if the inlet manifold is removed (the exhaust manifold can be examined as well for cracks etc. in the process). After the repairs check for fault codes again... but when the idle stepper motor was changed was the throttle cable adjusted?