Hi, I have a Mazda 3, I have a problem with the car and need help! The car on tick over is revving high and sounds like it has a cough all the time, its also really loud when im driving and it's getting worse, it also gets worse when I turn the aircon on. I've had it to 2 garages and both could see what I was saying but don't know what it is, both have plugged the computer in and all is fine, engine mounts are secure and nobody seems to know how to stop it!! Anybody with any ideas?

 

This could be an IAC valve sticking or a vacuum leak. It takes a while for the PCM to set the CEL.
Currently I am chasing down a similar issue with a Ford Contour. So far I cleaned the MAF sensor and the throttle body. Next I will clean the IAC valve.
I used MAF sensor cleaner to find vacuum leaks and it appears the intake manifold gasket or the fuel injectors might leak air into the intake.
All other vacuum lines seem to be ok. Make sure you check the PCV system.