I have a 2000 Madza MPV, giving codes P0175 (rich Air/fuel on bank 2) and...

Can these be tested? My mechanic said he has to remove the intake manifold to check the electric wire on the injector #5. The misfire was on cylinder #6 before. I sprayed MAF cleaner in the EGR small hole that is contected to a rubber hose. (i took out the hose and sparyed inside the EGR, the engine trembled),then the misfire became on #5 instead of #6. All sparkplugs are clean now but #5 gets dry black every time I change it.

All can be tested with the right tools and know how. Not putting your mechanic down, there are ways to do things, and some have their ways. Why are trying to ruin the diaphragm on the EGR. If it changed the RPM, better get a new one.

After I sprayed in the EGR hole, the RPM on idle became lower. I drove it. Then the next morning, the EGR hole (where I sprayed) became clogged, and I had it removed and cleaned. Should I buy a new EGR? Why did the misfire move from cylinder 6 to 5 after I sprayed?

If the diaphragm rotted with spray, it will not function properly. It operates with vacuum from the solenoid valve to open and close when the computer wants to enrich the fuel mixture while driving. I don't remember the position of the EGR valve, maybe closer to the #5 cylinder intake port. What ever was done it has effected #5 now more than #6. Both are probably still effected, the problem is still there. Yes replace the valve with a new one. Before you do something ask before it will cost you. The EGR could have been part of the problem anyway.