Toyota Repair: EGR System Code P0401, egr system, exhaust gas recirculation

Question
Hi Ted!
I got a problem my car is Toyota 2000 RAV4 4cyl
I got codes P0401 (AutoZone OBD2), Insufficient flow in the exhaust gas recirculation system,
Where/what should I start checking? I'd like to fix this myself (I have experience to fix Camaro and Audi A4)
but I don't know about Toyota Rav4.

the things I only did is :PCV VALVE (changed) and I have cleaned EGR Valve(with spray cleaner) , Throttle Body -Plate(with spray cleaner).

I ran the EGR Valve tests : I applied finger pressure directly to the EGR valve membrane while idling and the engine begin to stumble and almost die---> does it mean something? Is it good or bad?

what else could it be?

Thanks for your help!
sorry for my bad English

Answer
It means that the egr valve is working, the problem is a very common one, it's the egr modulator valve and to some extent the vacuum switching valve(VSV) for the egr valve, the modulator is attached to the egr valve, remove it and if air can pass from the bottom port through it is defective, in that case replace it and see if it takes care of the problem, if the valve is ok the egr
vsv should be replaced.