1990 Camry V6 Auto, Diagnostic Code 12, 71

I connect the E1 and T terminal to get diagnostic code 12 and 71. Code 12 is R.P.M signal. Where should I check ?
Code 71 is Exhaust gas recirculation sensor signal. Since the ERG system has 1) EGR control volve 2) EGR Vacuum Modulator and 3) ECM controlled Vacumm Switching Volve, VSV. How do I know which part is wrong?

The symptom of the car is; when driving for 10-20 minutes, somke will come out from hood. The car could not drive over 30 MPH and sometime even fully stop. The engine still running but the car won't move. Please refer to my preview Thread, 1990 Camry V6 Auto, smoke, stalling.

Your comments are highly appreciated.

Thank you in advance.
minlin

I had one experience with my customer like yours. His car start run but no power after about 10 minutes run the smoke start come out from the hood, after all the test i made it turn out to be a bad coil.

It could also be a stuck EGR valve.

sorry about dragging an old thread up.. but, what is the best course of action to take if u get a 71 code? take car to dealership, or to any mechanic, or what? also, what should i expect when i bring my car in? i'm worried i'll get totally ripped off, and not even know it. i imagine it'll be an expensive diagnosis, followed by "well, everything relating to the exhaust gas recirculation sensor signal is broken, plus your entire electrical system needs a rehaul, it will cost about forty to fifty thousand dollars." is this reasonable? or what?