Help: GM sensor/diagnostic experts

1994 Olds 88 Royale, 3800 V6, OBD-I (OBD-II connector), auto
BACKGROUND: intermittent MIL lamp. Clears on next start. History code is always P1406, EGR
pintle position error. PCM to EGR signal lines continuity check, good.
key on, running at idle, normal operating temp, tranny in park: EGR control line RA16 (also at EGR harness pin A), B+, good EGR +5 reference line WC10 (also at EGR harness pin D), 5.05V, good EGR pintle position BF12 (also at EGR harness pin C), .72V, good
road test, monitor DVOM voltage at EGR pintle position line at PCM (BF12): on accelleration, BF12 goes to 3-5V speed at 25-30mph, foot off accelerator, BF12 goes to .72 come to stop, BF12 is .72 feather foot the accel, BF12 drops to .35-.55V, before jumping to up to normal voltage, seconds later MIL sets.
QUESTION: what could cause the EGR pintle position signal to drop below .72v? Could another sensor like the TPS upset the reference voltage to the EGR valve?
Please advice. I am going out of my ever loving mind!
TIA Bill
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In addition: codes P0300, P0171, and P0172 have also been set in history along with P1406.

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You probably need to see what the desired and actual EGR position is on the scan tool to diagnose this very easily. However, the EGR being jammed with carbon seems a common cause of those kinds of problems - it can cause the pintle to jam open or hang up.
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Robert Hancock Saskatoon, SK, Canada
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I did a 30 minute run with log to the computer. The PCM was ordering the EGR open and closed like a yo yo. The EGR worked fine except trying to keep up with the stupid signals from the PCM. It was being caused by flaky connections at the PCM. Its fixed. Thanks for the reply.
I am relatively new to late model GM electronics. My experience is with older Mercedes, diesels, carbed Porsches, and other foreign crap. I like the GM products will just have eat some time and sweat with the learning curve.
Thanks for the help.
Bill
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The EGR pintle and valve area is clean. It seats perfectly.
I replaced the EGR with another known good unit: same results.
I dynamically scanned and plotted the operation of the EGR: the EGR %pos is continueally showing a value higher than 0, when in fact the EGR pos volts are at .72v, or the zero position. This error is realized after moving the car for the first time after startup.
I also routed new wires from the PCM to the EGR for circuits 435 (EGR control), 1456 (EGR pintle position) and 474 (EGR +5v ref): same problem.
The question: is the PCM the problem?
Bill
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