THERE IS NOT ONE.
on the 3.4L V6 it is located on the front valve cover, just to the right of the oil filler cap. there is a hose with a 90 degree boot on it. remove that and pull out the PCV valve.
There are many gaskets on any car engine. If you are asking about head gaskets, they are between the cylinder head(s) and the engine block. The cylinder head is under the valve cover. --------------
There is one intake valve for each cylinder. It is located in the top of the head. If you remove the valve cover, you can see the stem of the valves by peeking through the caps in the valve spring. If you want to replace a valve, it will be necessary to first remove the cylinder head.
Look on the front valve cover and it is to the right of the oil fill cap. There will be a black hose going to it that makes a 90 degree angle. Pull that off and then pull the PCV out.
Some of the 2000 models have a PCV valve on the back of the valve cover. The other models do not have a PCV valve, but use an oil/air separator instead.
In the transmission in front of the modulator
The 1989 Oldsmobile EGR valve is located on the top of the engine, near the back. It is quite simple to change.
Type your answer here... They are in the cylinder head.
Totally depends on engine. If you dont see them right off, your are most likely located under the big valve cover similar to the hemi engines of Chrysler.
The brake valve is located next to the master brake cylinder. The valve can be found just below the master brake cylinder.
There is no egr valve on a 1990 Mazda MPV 6 cylinder