does anybody have an idea how to install a blow off valve on a 99 A4. I am thinking to get one.

Thanks

 

Don't get it. These cars don't respond well to BOVs. Since the air the BOV purges has already been measured by the mass air meter, you'll get a rich spike when you shift because the car expects that air in the engine and is fueling for it. Over time the rich spiking on shifts will foul the cat and screw up the O2 sensors. Upgrade your DV (diverter valve) to an aftermarket one when you chip your car, and you'll be fine. Get a BOV, and you're asking for trouble down the road.

 

UpstateNYA4 is absolutely right!

Don't do it dude! If your car is fitted with a MAF it will also be fitted with a 'diverter valve'. This dumps air back into the inlet instead of to atmosphere, like a Dump Valve (or Blow Off Valve) would. This is because the air in the system has already been registered by the MAF and therefore Engine Management System as been passed to the engine. The rich spiking that UpstateNYA4 meantioned can also damage your CAT.

Hope this helps!