Toyota Repair: Toyota Previa 1993 check engin code 71, vacuum ports, vacuum gauge

Question
Hi Ted,

     I owned a 1993 Toyota Previa, when my check engin light on for code 71(RGB malfunction), I replace the modulator and RGB valve also check the hose to make sure not lasking, but light still on w/ code 71, the only parts left not replace is the EGR sensor but doesn't know where it locate. what are your thoughts?

Thanks     

Ray

Answer
The most common failure is the egr modulator, check the small vacuum ports on the throttle body on top they are marked P,R,Q make sure they are not clogged up, clean them out with a small wire and some spray cleaner, if you have a vacuum gauge check for vacuum at these ports with the engine between 1400-1800 rpm, the vacuum should be steady, this is a two stage system so one port will get vacuum at a lower speed the other port will get vacuum at higher rpm.
The temp sensor is located on the egr valve housing, it is almost never the cause.