i have an s4 engine in my s5.. noticed when i was installing the engine, that my vac. lines were hitting this thing and was not working.. so should i bend the lines or remove it... and when i bought the car it already had s4 motor.. never seen a s5 does the s5 have this??

 

That is the EGR valve. You'll need it to pass the visual part of the smog test, but is doesn't necessarily have to be working. You should leave in on the block to save yourself the headache every 2 years, but you can cap the lines if you want.

And you're right, S5s don't have EGR valves. Mazda got away with it for a few years, then had to bring it back on the FD. EGRs are virtually useless on rotaries. NOx levels are perfectly fine without one.

 

You should remove it.

When you take your car in for a smog, the technician looks up what emissions systems are supposed to be on the vehicle; by leaving the EGR on you will just confuse the technician and make his life harder because your engine is not supposed to have one. If he figures out it is there because you have an older block, it is in his power to fail your vehicle due to an illegal engine change.

If you do leave it on you might as well keep it operational as it will lower your NoX (better for mother earth), and will also help keep your combustion temps cooler thus having the possibility of preventing pre-detonation (pinging).

 

Hmm, I overlooked the part about the S4 engine being in an S5 car. In that case, I change my mind and agree it can be removed and blocked off. It's tucked under the UIM anyway, so chances are no one will notice the block-off plate.